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EDITED    BY 


ptoUseov  3.  »c*een  Cattell,  flD.B.,  t>b, 

AND 


COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 
AND  COMPARATIVE  PSYCHOLOGY 


Comparative  Physiology  of  the 

Brain  and  Comparative 

Psychology 


By 

Jacques  [Loeb,  M.D. 

Professor  of  Physiology  in  the  University  of  Chicago 


Illustrated 


New  York 

G.  P.  Putnam's  Sons 

London:  John  Murray 

I002 


Copyright,  1900 

BY 

G.  P.  PUTNAM'S  SONS 


Ube  'Rnicfierbocliec  presf,  flew  ^tft 


TO 

PROFESSOR  ERNST  MACH 


HHi:)l 


PREFACE 


It  is  the  purpose  of  this  book  to  serve  as  a  short 
introduction  to  the  comp3.rative  physiology  of  the 
brain  and  of  the  central  nervous  system. 

Physiology  has  thus  far  been  essentially  the  physi- 
ology of  Vertebrates.  I  am  convinced,  however,  that 
for  the  establishment  of  the  laws  of  life-phenomena 
a  broader  basis  is  necessary.  Such  a  basis  can  be 
furnished  only  by  a  comparative  physiology  which 
includes  all  classes  of  the  animal  kingdom.  My  ex- 
perience in  the  course  on  comparative  physiology 
at  Wood's  HoU  seems  to  indicate  that  the  transition 
from  the  old  to  the  comparative  physiology  can  be 
most  readily  accomplished  through  the  physiology  of 
the  central  nervous  system.  ^ 

The  physiology  of  the  brain  has  been  rendered 
unnecessarily  difficult  through  the  fact  that  meta- 
physicians have  at  all  times  concerned  themselves 
with  the  interpretation  of  brain  functions  and  have 
introduced  such  metaphysical  conceptions  as  soul, 
consciousness,  will,  etc.  One  part  of  the  work  of 
the  physiologist  must  consist  in  the  substitution  of 
real  physiological  processes  for  these  inadequate  con- 
ceptions.    Professor  Ernst  Mach,  of  Vienna,  to  whom 


vi  PREFACE 

this  book  is  dedicated,  was  the  first  to  establish  the 
general  principles  of  an  antimetaphysical  science. 

I  have  added  at  the  end  of  each  chapter  a  list  of 
the  chief  papers  of  which  I  have  made  use.  Although 
far  from  complete,  this  may  serve  the  beginner  as  a 
guide  for  the  further  study  of  the  subjects  touched 
upon. 

The  book  appeared  first  in  German  and  was  trans- 
lated by  Anne  Leonard  Loeb.  As  a  number  of  new 
facts  have  been  found  since  the  German  edition  ap- 
peared, and  as  it  seemed  desirable  to  formulate  my 
antimetaphysical  standpoint  more  precisely,  I  have 
made  extensive  alterations. 

My  thanks  are  due  to  a  number  of  friends  who 
have  offered  suggestions, — most  of  all  to  my  pupil, 
Miss  Anne  Moore. 

The  University  of  Chicago, 
October  i.  1900. 


CONTENTS 

CHAPTER  I. 

PAGB 

Some  Fundamental  Facts  and  Conceptions  Concern- 
ing THE  Comparative  Physiology  of  the  Cen- 
tral Nervous  System i 

CHAPTER  II. 
The  Central  Nervous  System  of  Medusae.     Experi- 
ments ON  Spontaneity  and  Coordination  .        .       i6 

CHAPTER  III. 
The  Central  Nervous  System  of  Ascidians  and  its 

Significance  in  the  Mechanism  of  Reflexes      .      35 

CHAPTER  IV. 

Experiments  on  Actinians 48 

CHAPTER  V. 

Experiments  on  Echinoderms 61 

CHAPTER  VI. 

Experiments  on  Worms 72 

CHAPTER  VII. 

Experiments  on  Arthropods loi 

CHAPTER  VIII. 
Experiments  on  Mollusks 128 

vii 


via 


CONTENTS 


CHAPTER  IX. 
The  Segmental  Theory  in  Vertebrates 

CHAPTER  X. 
Semidecussation  of  Fibres  and  Forced  Movements 

CHAPTER  XI. 
Relations  between  the  Orientation  and  Function  of 
Certain  Elements  of  the  Segmental  Ganglia 

CHAPTER  XII. 
Experiments  on  the  Cerebellum     .... 

CHAPTER  XIII. 
On  the  Theory  of  Animal  Instincts 

CHAPTER  XIV. 
The  Central  Nervous  System  and  Heredity 

CHAPTER  XV. 

The  Distribution  of  Associative  Memory  in  the  Ani 
MAL  Kingdom 

CHAPTER  XVI. 

Cerebral  Hemispheres  and  Associative  Memory  . 

CHAPTER  XVII. 
Anatomical  and  Psychic  Localisation  . 

CHAPTER  XVIII. 
Disturbances  of  Associative  Memory     . 

CHAPTER  XIX. 

On  Some  Starting-Points  for  a  Future  Analysis  of 
THE  Mechanics  of  Associative  Memory 

Index  


PAGS 


160 

213 
236 

277 
289 


ILLUSTRATIONS    IN   THE    TEXT 

FIGURE  PACK 

1.  Hydromedusa  (Gonionemus  Vertens) 17 

2.  Diagram  of  the  Bell  of  Aurelia  Aurita,     (After  Claus.)    .  18 

3.  Experiment  in  Dividing  a  Hydromedusa 19 

4.  Arrangement  for  Producing  Automatically  Pulsating  Air- 

Bubbles    21 

5.  Dr.  Hargitt's  Experiment 27 

6.  Diagram  of  the  Ascidian  Heart        .        .        .        .        .        .28 

7.  Localising  Reflex  in  Tiaropsis  Indicans 31 

8.  Diagram  for  Explaining  the  Localising  Reflex  in  Medusa  32 

9.  ClONA  Intestinalis 36 

10.  The  Ability  of  the  Actinians  to  Discriminate        ...  49 

11.  Continuation  of  the  Experiment  in  Fig.  10     ....  50 

12.  An  Actinian  (Cerianthus)  with  a  Normal  Head  and  with 

an  Artificially  Produced  Head 52 

13.  An  Actinian  (Cerianthus)  that  had  been  Placed  in  a  Test- 

TuBE,  Head  down,  Regaining  its  Normal  Orientation     .  55 

14.  Cerianthus  Regaining  its  Normal  Orientation      .        .        .57 

15.  Actinian  that  has  been  Forced  by  Gravitation  to   Push 

itself  through  a  Wire  Net  Three  Times   ....  59 

16.  Nervous  System  of  a  Starfish  ....                .        .  61 

17.  Mechanism  of  the  Turning  of  a  Starfish  that  has  been  Laid 

ON  its  Back 62 

18.  The  Same  Experiment  on  a  Starfish  whose  Nerve-Ring  has 

been  Severed  in  Two  Places 63 

19.  Geotrgpic  Reaction  OF  CucuM ARIA  Cucumis      .        .        .        .67 

ix 


X  ILLUSTRATIONS  IN   THE   TEXT 

FIGURE  PAGE 

20.  ThysanozoOn  Brocchii,  a  Marine  Planarian   ....  72 

21.  Thysanozoon  Divided  Transversely 73 

22.  ThysanozoOn  with  Transverse  Incision 75 

23.  Fresh- Water  Planarian  (Planaria  Torva)       ....  77 

24.  Two-Headed    Planarian    Produced  Artificially.      (After 

van  Duyne.) 81 

25.  Planarian  with  Two  Heads  that  are  Attempting  to  Move 

IN  Opposite  Directions,  and  in  so  Doing  are  Tearing 
the  Common  Body.    (After  van  Duyne.)     ....      82 

26.  The  Brain  and  a  Series  of  Segmental  Ganglia  of  an  An- 

nelid (Nereis) 83 

27.  Dorsal  View  of  the  Central  Nervous  System  of  an  Earth- 

worm  84 

28.  Side  View  of  the  Central  Nervous  System  of  the  Earth- 

worm         85 

29.  A  Group  of  Nereis  whose  Brains  have  been  Removed.    They 

AT  Last  Collect  in  a  Corner  of  the  Aquarium  and  Perish 
in  the  Vain  Attempt  to  Go  through  the  Glass.  (After 
Maxwell.) 93 

30.  Head  of  Nereis.     (After  Quatrefages.) 98 

31.  LiMULUs   Polyphemus   with   the  Central  Nervous  System 

Exposed 103 

32.  Lobster  with  Central  Nervous  System  Exposed     .        .        .115 

33.  Diagrammatic    Representation    of    the    Central  Nervous 

System  of  a  Snail  (Paludina  Vivipara)        ....     128 

34.  Brain  of  Sepia 129 

35.  The  Frog's  Brain 139 

36.  Position  of  the  Appendages  of  Limulus  after  Destruction 

OF  the  Right  Half  of  the  Brain 156 

37.  Attitude  of  an  Amblystoma  under  the  Influence  of  a  Gal- 

vanic Current  Passing  from  Head  to  Tail         .        .        .     160 

38.  Attitude  of  an  Amblystoma  when  the  Galvanic  Current 

Passes  from  Tail  to  Head 160 

39.  Cerebral  Hemispheres  of  a  Dog 260 


COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 
AND  COMPARATIVE  PSYCHOLOGY 


INTRODUCTION  TO 

HE  COMPARATIVE   PHYSIOLOGY 
OF  THE  BRAIN 


CHAPTER  I 

iOME  FUNDAMENTAL  FACTS  AND  CONCEPTIONS 
CONCERNING  THE  COMPARATIVE  PHYSIO- 
LOGY OF  THE  CENTRAL  NERVOUS  SYSTEM 

I.  The  understanding  of  complicated  phenomena 
lepends  upon  an  analysis  by  which  they  are  resolved 
into  their  simple  elementary  components.     If  we  ask 
^hat  the  elementary  components  are  in  the  physio- 
logy of  the  central  nervous  system,  our  attention  is 
iirected  to  a  class  of  processes  which  are  called  re- 
lexes.     A  reflex  is  a  reaction  which  is  caused  by  an 
[external  stimulus,  and  which  results  in  a  coordinated 
lovement,  the  closing  of  the   eyelid,    for   example, 
^hen  the  conjunctiva  is  touched  by  a  foreign  body, 
►r  the  narrowing  of  the  pupil  under  the  influence  of 
light.     In  each  of  these  cases,  changes  in  the  sensory 


2     COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

nerve-endings  are  produced  which  bring  about  a 
change  of  condition  in  the  nerves.  This  change 
travels  to  the  central  nervous  system,  passes  from 
there  to  the  motor  nerves,  and  terminates  in  the 
muscle-fibres,  producing  there  a  contraction.  This 
passage  from  the  stimulated  part  to  the  central 
nervous  system,  and  back  again  to  the  peripheral 
muscles,  is  called  a  reflex.  There  has  been  a  growing 
tendency  in  physiology  to  make  reflexes  the  basis  of 
the  analysis  of  the  functions  of  the  central  nervous 
system,  consequently  much  importance  has  been  at- 
tached to  the  underlying  processes  and  the  necessary 
mechanisms. 

The  name  reflex  suggests  a  comparison  between 
the  spinal  cord  and  a  mirror.  Sensory  stimuli  were 
supposed  to  be  reflected  from  the  spinal  cord  to  the 
muscles ;  destruction  of  the  spinal  cord  would,  ac- 
cording to  this,  make  the  reflex  impossible,  just  as 
the  breaking  of  the  mirror  prevents  the  reflection  of 
light.  This  comparison,  however,  of  the  reflex  pro- 
cess in  the  central  nervous  system  with  the  reflection 
of  light  has,  long  since,  become  meaningless,  and  at 
present  few  physiologists  in  using  the  term  reflex 
think  of  its  original  significance.  Instead  of  this, 
another  feature  in  the  conception  of  the  term  reflex 
has  gained  prominence,  namely,  the  purposeful  char- 
acter of  many  reflex  movements.  The  closing  of  the 
eyelid  and  the  narrowing  of  the  pupil  are  eminently 
purposeful,  for  the  cornea  is  protected  from  hurtful 
contact  with  foreign  bodies,  and  the  retina  from  the 


FUNDAMENTAL  FACTS  % 

injurious  effects  of  strong  light.  Another  striking 
characteristic  in  such  reflexes  has  also  been  empha- 
sised. The  movements  which  are  produced  are  so 
well  planned  and  coordinated  that  it  seems  as  though 
some  intelligence  were  at  work  either  in  devising  or 
in  carrying  them  out.  The  fact,  however,  that  a  de- 
capitated frog  will  brush  a  drop  of  acetic  acid  from 
its  skin,  suggests  that  some  other  explanation  is 
necessary.  A  prominent  psychologist  has  maintained 
that  reflexes  are  to  be  considered  as  the  mechanicaP^ 
effects  of  acts  of  volition  of  past  generations.  The  j 
ganglion-cell  seems  the  only  place  where  such  me- 
chanical effects  could  be  stored  up.  It  has  there- 
fore been  considered  the  most  essential  element  of 
the  reflex  mechanism,  the  nerve-fibres  being  regarded, 
and  probably  correctly,  merely  as  conductors. 

Both  the  authors  who  emphasise  the  purposeful- 
ness  of  the  reflex  act,  and  those  who  see  in  it  only  a 
physical  process,  have  invariably  looked  upon  the 
ganglion-cell  as  the  principal  bearer  of  the  structures 
for  the  complex  coordinated  movements  in  reflex 
action. 

I  should  have  been  as  little  inclined  as  any  other 
physiologist  to  doubt  the  correctness  of  this  concep- 
tion had  not  the  establishment  of  the  identity  of  the 
reactions  of  animals  and  plants  to  light  proved  the 
untenability  of  this  view  and  at  the  same  time  offered 
a  different  conception  of  reflexes.  The  flight  of 
the  moth  into  the  flame  is  a  typical  reflex  process. 
The  light  stimulates  the  peripheral  sense  organs,  the 


4     COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

stimulus  passes  to  the  central  nervous  system,  and 
from  there  to  the  muscles  of  the  wings,  and  the  moth 
is  caused  to  fly  into  the  flame.  This  reflex  process 
agrees  in  every  point  with  the  heliotropic  effects  of 
light  on  plant  organs.  Since  plants  possess  no  nerves, 
this  identity  of  animal  with  plant  heliotropism  can 
offer  but  one  inference  — these  heliotropic  effects  must 
depend  upon  conditions  which  are  common  to  both 
animals  and  plants.  At  the  end  of  my  book  on  helio- 
tropism I  expressed  this  view  in  the  following  words  : 
**  We  have  seen  that,  in  the  case  of  animals  which 
possess  nerves,  the  movements  of  orientation  toward 
light  are  governed  by  exactly  the  same  external  con- 
ditions, and  depend  in  the  same  way  upon  the  external 
form  of  the  body,  as  in  the  case  of  plants  which  possess 
no  nerves.  These  heliotropic  phenomena,  conse- 
quently, cannot  depend  upon  specific  qualities  of  the 
central  nervous  system  (i)."  On  the  other  hand, 
the  objection  has  been  raised  that  destruction  of  the 
ganglion-cells  interrupts  the  reflex  process.  This 
argument,  however,  is  not  sound,  for  the  nervous 
reflex  arc  in  higher  animals  forms  the  only  protoplas- 
mic bridge  between  the  sensory  organs  of  the  surface 
of  the  body  and  the  muscles.  If  we  destroy  the  gan- 
glion-cells or  the  central  nervous  system,  we  interrupt 
the  continuity  of  the  protoplasmic  conduction  between 
the  surface  of  the  body  and  the  muscles,  and  a  reflex 
is  no  longer  possible.  Since  the  axis-cylinders  of  the 
nerves  and  the  ganglion-cells  are  nothing  more  than 
protoplasmic  formations,  we  are  justified  in  seeking 


FUNDAMENTAL  FACTS  5 

in  them  only  general  protoplasmic  qualities,  unless  we 
find  that  the  phenomena  cannot  be  explained  by 
means  of  the  latter  alone. 

2.  A  further  objection  has  been  raised,  that  al- 
though these  reflexes  occur  in  plants  possessing  no 
nervous  system,  yet  in  animals  where  ganglion-cells 
are  present  the  very  existence  of  ganglion-cells  neces- 
sitates the  presence  in  them  of  special  reflex  mechan- 
isms. It  was  therefore  necessary  to  find  out  if  there 
were  not  animals  in  which  coordinated  reflexes  still  ^ 
continued  to  exist  after  the  destruction  of  the  central 
nervous  system.  Such  a  phenomenon  could  be  ex- 
pected only  in  forms  in  which  a  direct  transmission  of 
stimuli  from  the  skin  to  the  muscle  is  possible,  in 
addition  to  the  transmission  through  the  reflex  arc. 
This  is  the  case,  for  instance,  in  worms  and  in  Ascidi- 
ans.  I  succeeded  in  demonstrating  in  Ciona  intesti- 
nalis  that  the  complicated  reflexes  still  continue  after 
removal  of  the  central  nervous  system  (2). 

A  study,  then,  of  comparative  physiology  brings 
out  the  fact  that  irritability  and  conductibility  are  the  I 
only  qualities  essential  to  reflexes,  and  these  are  both/ 
common   qualities  of  all  protoplasm.     The   irritable\ 
structures  at  the  surface  of  the  body,  and  the  arrange-    ) 
ment  of  the  muscles,  determine  the  character  of  the     I 
reflex  act.     The  assumption  that  the  central  nervous 
system  or  the  ganglion-cells  are  the  bearers  of  reflex 
mechanisms  cannot  hold.     But  have  we  now  to  con- 
clude that  the  nerves  are  superfluous  and  a  waste  ? 
Certainly  not.     Their  value  lies  in  the  fact  that  they 


6     COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

are  quicker  and  more  sensitive  conductors  than  undif- 
ferentiated protoplasm.  Because  of  these  quaHties  of 
the  nerves,  an  animal  is  better  able  to  adapt  itself  to 
changing  conditions  than  it  possibly  could  if  it  had 
no  nerves.  Such  power  of  adaptation  is  absolutely 
necessary  for  free  animals. 

3.  While  some  authors  explain  all  reflexes  on  a 
psychical  basis,  the  majority  of  investigators  explain  in 
this  way  only  a  certain  group  of  reflexes  —  the  so- 
called  instincts.  Instincts  are  defined  in  various  ways, 
but  no  matter  how  the  definition  is  phrased  the  mean- 
ing seems  to  be  that  they  are  inherited  reflexes  so 
purposeful  and  so  complicated  in  character  that  no- 
thing short  of  intelligence  and  experience  could  have 
produced  them.  To  this  class  of  reflexes  belongs 
the  habit  possessed  by  certain  insects  of  laying  their 
eggs  on  the  material  which  the  larvae  will  afterwards 
require  for  food.  When  we  consider  that  the  female 
fly  pays  no  attention  to  her  eggs  after  laying  them,  we 
cannot  cease  to  wonder  at  the  seeming  care  which 
nature  takes  for  the  preservation  of  the  species.  How 
can  the  action  of  such  an  insect  be  determined  if  not 
by  mysterious  structures  which  can  only  be  contained 
in  the  ganglion-cells  ?  How  can  we  explain  the  in- 
heritance of  such  instincts  if  we  believe  it  to  be  a 
fact  that  the  ganglion-cells  are  only  the  conductors 
of  stimuli  ?  It  was  impossible  either  to  develop  a 
mechanics  of  instincts  or  to  explain  their  inheritance 
in  a  simple  way  from  the  old  standpoint,  but  our  con- 
ception makes  an  explanation  possible.       Among  the 


r 


FUNDAMENTAL  FACTS  7 

elements  which  compose  these  complicated  instincts, 
the  tropisms  (heliotropism,  chemotropism,  geotropism, 
stereotropism)  play  an  important  part.  These  trop- 
isms are  identical  for  animals  and  plants.  The 
explanation  of  them  depends  first  upon  the  specific 
irritability  of  certain  elements  of  the  body-surface, 
and,  second,  upon  the  relations  of  symmetry  of  the 
body.  Symmetrical  elements  at  the  surface  of  the 
body  have  the  same  irritability ;  unsymmetrical  ele- 
ments have  a  different  irritability.  Those  nearer  the 
oral  pole  possess  an  irritability  greater  than  that  of 
those  near  the  aboral  pole.  These  circumstances 
force  an  animal  to  orient  itself  toward  a  source  of 
stimulation  in  such  a  way  that  symmetrical  points  on 
the  surface  of  the  body  are  stimulated  equally.  In 
this  way  the  animals  are  led  without  will  of  their  own 
either  toward  the  source  of  the  stimulus  or  away 
from  it.  Thus  there  remains  nothing  for  the  ganglion- 
cell  to  do  but  to  conduct  the  stimulus,  and  this  may 
be  accomplished  by  protoplasm  in  any  form.  For 
the  inheritance  of  instincts  it  is  only  necessary  that 
the  ^gg  contain  certain  substances  —  which  will  de- 
termine the  different  tropisms  —  and  the  conditions 
for  producing  bilateral  symmetry  of  the  embryo.  The 
mystery  with  which  the  ganglion-cell  has  been  sur- 
rounded has  led  not  only  to  no  definite  insight  into 
these  processes,  but  has  proved  rather  a  hindrance  in 
the  attempt  to  find  the  explanation  of  them. 

It  is  evident  that  there  is  no  sharp  line  of  demarc- 
ation between  reflexes  and  instincts.     We  find  that 


8     COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

authors  prefer  to  speak  of  reflexes  in  cases  where 
the  reaction  of  single  parts  or  organs  of  an  animal 
to  external  stimuli  is  concerned  ;  while  they  speak 
of  instincts  where  the  reaction  of  the  animal  as  a 
whole  is  involved  (as  is  the  case  in  tropisms). 

4.  If  the  mechanics  of  a  number  of  instincts  is 
explained  by  means  of  the  tropisms  common  to  ani- 
mals and  plants,  and  if  the  significance  of  the  gan- 
glion-cells is  confined,  as  in  all  reflex  processes,  to  their 
power  of  conducting  stimuli,  we  are  forced  to  ask 
what  circumstances  determine  the  coordinated  move- 
ments in  reflexes,  especially  in  the  more  complicated 
ones.  The  assumption  of  complicated  but  unknown 
and  perhaps  unknowable  structures  in  the  ganglion- 
cells  served  formerly  as  a  convenient  terminus  for  all 
thought  in  this  direction.  In  giving  up  this  assump- 
tion, we  are  called  upon  to  show  what  conditions  are 
able  to  determine  the  coordinated  character  of  reflex 
movements.  Experiments  on  galvanotropism  of  ani- 
mals have  proved  that  a  simple  relation  must  exist 
between  the  orientation  of  certain  motor  elements  in 
the  central  nervous  system  and  the  direction  of  the 
movements  of  the  body  which  is  called  forth  by  the 
activity  of  these  elements.  This  perhaps  creates  a 
rational  basis  for  the  further  investigation  of  coordi- 
nated movements. 

5.  We  must  also  deprive  the  ganglion-cells  of  all 
specific  significance  in  spontaneous  movements,  just 
as  we  have  done  in  the  case  of  simple  reflexes  and 
instincts.      By    spontaneous    movements    we    mean 


FUNDAMENTAL  FACTS  9 

movements  which  are  apparently  determined  by  inter- 
nal conditions  of  the  living  system.  Strictly  speaking, 
no  movements  of  animals  are  exclusively  determined 
by  internal  conditions,  for  the  atmospheric  oxygen 
and  a  certain  temperature  or  certain  limits  of  tem- 
perature are  always  necessary  in  order  to  preserve 
the  activity  beyond  a  short  period  of  time. 

We  must  discriminate  between  simple  and  conscious 
spontaneity.  In  simple  spontaneity  we  must  consider 
two  kinds  of  processes,  namely,  aperiodic  spontaneous 
processes  and  rhythmically  spontaneous  or  automatic 
processes.  The  rhythmical  processes  are  of  import- 
ance for  our  consideration.  Respiration  and  the 
heart-beat  belong  to  this  category.  The  respiratory 
movements  prove  without  possible  doubt  that  auto- 
matic activity  can  arise  in  the  ganglion-cells,  and 
from  this  the  conclusion  has  been  drawn  that  all 
automatic  movements  are  due  to  specific  structures 
of  the  ganglion-cells.  Recent  investigations,  how- 
ever, have  transferred  the  problem  of  rhythmical 
spontaneous  contractions  from  the  field  of  morphology 
into  that  of  physical  chemistry.  The  peculiar  quali- 
ties of  each  tissue  are  partly  due  to  the  fact  that  it 
contains  Ions  (Na,  K,  Ca,  and  others)  In  definite 
proportions.  By  changing  these  proportions,  we  can 
impart  to  a  tissue  properties  which  it  does  not  ord- 
inarily possess.  If  In  the  muscles  of  the  skeleton 
the  Na  ions  be  increased  and  the  Ca  Ions  be  reduced, 
the  muscles  are  able  to  contract  rhythmically,  like  the 
heart.     It  Is   only  the   presence  of   Ca  ions  in    the 


10    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

blood  which  prevents  the  muscles  of  our  skeleton 
from  beating  rhythmically  in  our  body.  As  the  mus- 
cles contain  no  ganglion-cells,  it  is  certain  that 
the  power  of  rhythmical  spontaneous  contractions 
is  not  due  to  the  specific  morphological  character 
of  the  ganglion-cells,  but  to  definite  chemical  con- 
ditions which  are  not  necessarily  confined  to  gang- 
lion-cells (3). 

The  coordinated  character  of  automatic  movements 
has  often  been  explained  by  a  *'  centre  of  coordina- 
tion," which  is  supposed  to  keep  a  kind  of  police 
watch  on  the  different  elements  and  see  that  they 
move  in  the  right  order.  Observations  in  lower 
animals,  however,  show  that  the  coordination  of 
automatic  movements  is  caused  by  the  fact  that 
that  element  which  beats  most  quickly  forces  the 
others  to  beat  in  its  own  rhythm.  Aperiodic 
spontaneity  is  still  less  a  specific  function  of  the  gang- 
lion-cell than  rhythmical  spontaneity.  The  swarm- 
spores  of  algae,  which  possess  no  ganglion-cells, 
show  spontaneity  equal  to  that  of  animals  having 
ganglion-cells. 

6.  Thus  far  we  have  not  touched  upon  the  most 
important  problem  in  physiology,  namely,  which 
mechanisms  give  rise  to  that  complex  of  phenomena 
which  are  called  psychic  or  conscious.  Our  method 
of  procedure  must  be  the  same  as  in  the  case  of  in- 
stincts and  reflexes.  We  must  find  out  the  ele- 
mentary physiological  processes  which  underlie  the 
complicated    phenomena    of    consciousness.       Some 


FUNDAMENTAL  FACTS  ii 

physiologists  and  psychologists  consider  the  purpose- 
fulness  of  the  psychic  action  as  the  essential  element. 
If  an  animal  or  an  organ  reacts  as  a  rational  man 
would  do  under  the  same  circumstances,  these  authors 
declare  that  we  are  dealing  with  a  phenomenon  of 
consciousness.  In  this  way  many  reflexes,  the  in- 
stincts especially,  are  looked  upon  as  psychic  func- 
tions. Consciousness  has  been  ascribed  even  to  the 
spinal  cord,  because  many  of  its  functions  are  pur- 
poseful. We  shall  see  in  the  following  chapters 
that  many  of  these  reactions  are  merely  tropisms 
which  may  occur  in  exactly  the  same  form  in  plants. 
Plants  must  therefore  have  a  psychic  life,  and,  follow- 
ing the  argument,  we  must  ascribe  it  to  machines 
also,  for  the  tropisms  depend  only  on  simple  mechan- 
ical arrangements.  In  the  last  analysis,  then,  we 
would  arrive  at  molecules  and  atoms  endowed  with 
mental  qualities. 

We  can  dispose  of  this  view  by  the  mere  fact  that 
the  phenomena  of  embryological  development  and  of 
organisation  in  general  show  a  degree  of  purposeful- 
ness  which  may  even  surpass  that  of  any  reflex  or 
instinctive  or  conscious  act.  And  yet  we  do  not 
consider  the  phenomena  of  development  to  be  depend- 
ent upon  consciousness. 

On  the  other  hand,  physiologists  who  have  appre- 
ciated the  untenable  character  of  such  metaphysical 
speculations  have  held  that  the  only  alternative  is 
to  drop  the  search  for  the  mechanisms  underlying 
consciousness  and   study  exclusively  the   results   of 


12    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

operations  on  the  brain.  This  would  be  throw- 
ing out  the  wheat  with  the  chaff.  The  mis- 
take made  by  metaphysicians  is  not  that  they 
devote  themselves  to  fundamental  problems,  but 
that  they  employ  the  wrong  methods  of  invest- 
igation and  substitute  a  play  on  words  for  ex- 
planation by  means  of  facts.  If  brain-physiology 
gives  up  its  fundamental  problem,  namely,  the  dis- 
covery of  those  elementary  processes  which  make 
consciousness  possible,  it  abandons  its  best  possi- 
bilities. But  to  obtain  results,  the  errors  of  the 
metaphysician  must  be  avoided  and  explanations 
must  rest  upon  facts,  not  words.  The  method  should 
be  the  same  for  animal  psychology  that  it  is  for 
brain-physiology.  It  should  consist  in  the  right 
understanding  of  the  fundamental  process  which  re- 
curs in  all  psychic  phenomena  as  the  elemental  com- 
ponent. This  process,  according  to  my  opinion,  is  the 
activity  of  the  associative  memory,  or  of  association. 
Consciousness  is  only  a  metaphysical  term  for 
phenomena  which  are  determined  by  associative 
memory.  By  associative  memory  I  mean  that 
mechanism  by  which  a  stimulus  brings  about  not 
only  the  effects  which  its  nature  and  the  specific 
structure  of  the  irritable  organ  call  for,  but  by  which 
it  brings  about  also  the  effects  of  other  stimuli  which 
formerly  acted  upon  the  organism  almost  or  quite 
simultaneously  with  the  stimulus  in  question  (4).  If 
an  animal  can  be  trained,  if  it  can  learn,  it  possesses 
associative  memory.      By  means  of  this  criterion  it 


FUNDAMENTAL  FACTS 


13 


can  be  shown  that  Infusoria,  Coelenterates,  and 
worms  do  not  possess  a  trace  of  associative  memory. 
Among  certain  classes  of  insects  (for  instance, 
wasps),  the  existence  of  associative  memory  can  be 
proved.  It  is  a  comparatively  easy  task  to  find  out 
which  representatives  of  the  various  classes  of  ani- 
mals possess,  and  which  do  not  possess,  associative 
memory.  Our  criterion  therefore  might  be  of 
great  assistance  in  the  development  of  comparative 
psychology. 

7.  Our  criterion  puts  an  end  to  the  metaphysical 
ideas  that  all  matter,  and  hence  the  whole  animal 
world,  possesses  consciousness.  We  are  brought  to 
the  theory  that  only  certain  species  of  animals  possess 
associative  memory  and  have  consciousness,  and  that 
it  appears  in  them  only  after  they  have  reached 
a  certain  stage  in  their  ontogenetic  development. 
This  is  apparent  from  the  fact  that  associative 
memory  depends  upon  mechanical  arrangements 
which  are  present  only  in  certain  animals,  and 
present  in  these  only  after  a  certain  develop- 
ment has  been  reached.  The  fact  that  certain  ver- 
tebrates lose  all  power  of  associative  memory  after 
the  destruction  of  the  cerebral  hemispheres,  and 
the  fact  that  vertebrates  in  which  the  associative 
memory  either  is  not  developed  at  all  or  only  slightly 
developed  {e.  g.,  the  shark  or  frog)  do  not  differ,  or 
differ  but  slightly,  in  their  reactions  after  losing  the 
cerebral  hemispheres,  support  this  view.  The  fact 
that   only   certain    animals    possess    the    necessary 


14    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

mechanical  arrangements  for  associative  memory, 
and  therefore  for  metaphysical  consciousness,  is  not 
stranger  than  the  fact  that  only  certain  animals 
possess  the  mechanical  arrangements  for  uniting  the 
rays  from  a  luminous  point  in  one  point  on  the 
retina.  The  liquefaction  of  gases  is  an  example  of  a 
sudden  change  of  condition  which  may  be  produced 
when  one  variable  is  changed  ;  it  is  not  surprising 
that  there  should  be  sudden  changes  in  the  onto- 
genetic and  phylogenetic  development  of  organisms 
when  there  are  so  many  variables  subject  to  change, 
and  when  we  consider  that  colloids  easily  change 
their  state  of  matter. 

It  becomes  evident  that  the  unravelling  of  the 
mechanism  of  associative  memory  is  the  great  dis- 
covery to  be  made  in  the  field  of  brain-physiology 
and  psychology.  But  at  the  same  time  it  is  evident 
that  this  mechanism  cannot  be  unravelled  by  histo- 
logical methods,  or  by  operations  on  the  brain,  or  by 
measuring  reaction  times.  We  have  to  remember 
that  all  life  phenomena  are  ultimately  due  to  motions 
or  changes  occurring  in  colloidal  substances.  The 
question  is.  Which  peculiarities  of  the  colloidal  sub- 
stances can  make  the  phenomenon  of  associative 
memory  possible  ?  For  the  solution  of  this  problem 
the  experience  of  physical  chemistry  and  of  the 
physiology  of  the  protoplasm  must  be  combined. 
From  the  same  sources  we  must  expect  the  solution 
of  the  other  fundamental  problems  of  brain-physio- 
logy, namely,  the  process  of  conduction  of  stimuli. 


FUNDAMENTAL  FACTS  15 

Bibliography. 

1.  LoEB,  J.  Der  Heliotropismus  der  Thiere  und  seine  Ueberein- 
stimmung  mit  dem  Heliotropismus  der  Pflanzen.  WUrzburg, 
1890.  A  preliminary  note  on  ihese  experiments  appeared 
January,  1888. 

2.  LoEB,  J.  Uniersuchungen  zur  physiologischen  Morphologie 
der  Thiere  II.     WUrzburg,  1892. 

3.  LoEB,  J.  American  Journal  of  Physiology ^  vol.  iii.,  p.  327 
and  p.  383,  1900. 

4.  LoEB,  J.  Bettrdge  zur  Gehirnphysiologie  der  Wiirmer, 
P finger's  ArchiVy  Band  Ivi.,  1894. 


I 


CHAPTER  II 

THE  CENTRAL  NERVOUS  SYSTEM  OF  MEDUSAE. 
EXPERIMENTS  ON  SPONTANEITY  AND  CO- 
ORDINATION 

I.  Experiments  on  Medusae  or  jelly-fish  afford 
us  an  excellent  opportunity  for  analysing  the  con- 
ditions for  spontaneity  and  coordination,  and  for 
deciding  whether  or  not  these  phenomena  are  depend- 
ent upon  ganglion-cells.  The  subumbrella  of  the 
Medusae  has  a  very  thin  layer  of  muscle-fibres  which 
contract  rhythmically.  The  contraction  diminishes 
the  size  of  the  swimming-bell,  and  forces  the  water 
out.  By  means  of  the  recoil  the  animal  moves  for- 
ward. In  regard  to  the  nervous  system,  we  must 
discriminate  between  two  classes  of  Medusae  :  first, 
the  Hydromedusae  (Hydroidea,  Fig.  i),  and,  second, 
the  Acalephae,  one  representative  of  which  (Aurelza 
aurita,  Fig.  2)  is  familiar  to  many  laymen.  The 
nervous  system  of  the  Hydromedusae  consists  of  a 
double  nerve-ring  along  the  margin  of  the  umbrella 
{d,  Fig.  i).  The  upper  nerve-ring  forms  a  flat  layer 
in  the  ectoderm,  and  consists  of  thin  fibres  and  gan- 
glion-cells.    The  lower  nerve-ring  has  thicker  fibres 

16 


EXPERIMENTS  ON  MEDUSAE 


17 


and  more  ganglion-cells,  and  is  connected  with  the 
upper  ring  by  nerve-fibres.  In  addition  to  this  ring, 
which  is  called  the  central  nervous  system,  there  is 
also  a  peripheral  nerv- 
ous system,  a  plexus, 
consisting  of  nerves 
and  scattered  ganglion 
cells,  spread  out  over 
the  whole  subumbrella 
{b,  Fig.  i),  between 
the  epithelium  and 
the  muscle-layer.  The 
convex  surface  of  the 
umbrella  consists  of  a 
non-contractile,  gelat- 
inous mass,  and  no 
nervous  elements  are 
to  be  found  in  it. 

Acalephse  (Fig.  2) 
have  no  continuous 
nerve-ring,  but  a  row  of  separate  nerve-centres  {S,  Fig. 
2)  extends  around  the  margin  of  t^e  umbrella,  lying  in 
the  ectoderm,  which  covers  the  basis  of  the  marginal 
bodies  (sense  organs).  The  number  of  these  centres 
corresponds,  at  least  in  Aurelia  aurita^  with  the  num- 
ber of  sense  organs.  This  nervous  system  contains 
no  ganglion-cells,  but  processes  called  nerve-fibres  go 
out  from  special  epithelial  cells.  The  muscle-layer 
of  the  umbrella  also  is  said  to  contain  a  peripheral 
nervous  plexus  (i). 


Fig.  I. 


(Gonionemus 


Hydromedusa. 
vertens.) 

a,  umbrella ;  b^  subumbrella  with  muscles ;  c,  man- 
ubrium ;  d^  margin  of  the  swimming-bell  with  the 
nerve-ring. 


i8    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

Our  first  question  is  :  Is  the  spontaneous  locomo- 
tion of  the  Medusae,  or  the  rhythmical  contraction  of 
their  swimming-bell,  a  function  of  the  ganglion-cells  ? 

©Romanes        found 
w    that  if  the  margin  of 
the  bell  of  a  Hydro- 
. .  *  *  medusa  {b,  Fig.  3)  be 

cut  off,  the  rhythmical 
contraction  of  the 
centre  of  the  bell  {a, 
Fig.   3)  ceases,  while 

Fig.  2.    Diagram  of  the  Bell  of  Aurelia    \\\^   marp"in    b     which 
AuRiTA,  WITH  Eight  Sense  Organs. 


(After  Claus.) 


contains  the  nerve- 
ring,  continues  to  ex- 
ecute rhythmical  contractions  (2).  The  wound  does 
not  even  cause  a  decrease  in  the  number  or  in  the 
strength  of  the  marginal  contractions.  The  exper- 
iment has  been  repeated  by  other  authors  with  the 
same  result.  Any  sort  of  wound  can  be  made  in 
the  umbrella  without  disturbing  the  rhythmical  con- 
tractions so  long  as  the  nerve-ring  remains  intact. 
Thus  Romanes  concluded  that  these  rhythmical  con- 
tractions of  Hydromedusse  originate  in  the  nerve- 
ring  or  its  ganglia.  I  have  found  recently  that  this 
whole  problem  is  not  so  much  a  morphological  problem 
as  a  problem  of  physical  chemistry.  The  osmotic 
pressure  of  the  sea-water  is  about  equal  to  that  of  a 
-|  n  NaCl  solution.  I  found  that  if  the  centre  of  a 
swimming-bell  be  put  into  a  f  n  NaCl  or  -|  n  NaBr 
solution  it  goes  on  beating  rhythmically.     But  if  a 


EXPERIMENTS  ON  MEDUSA 


19 


small  quantity  of  CaCl^  or  KCl,  or  both,  be  added, 
the  centre  stops  beating.  The  centre  would  beat  in 
sea-water  were  it  not  for  the  presence  there  of  Ca,  K, 
and  possibly  other  ions  (3). 
The  centre  contains  some 
scattered  ganglion-cells.  It 
might  be  argued  that  the 
presence  of  these  cells  makes 
the  rhythmical  contractions 
in  a  pure  NaCl  solution  pos- 
sible. It  is  easy  to  prove 
that  such  is  not  the  case. 
The  striped  skeletal  muscles 
of  a  frog  do  not  contract 
rhythmically  in  blood  or 
serum.  I  have  shown  that 
this  is  due  to  the  presence 
of  Ca  ions  in  these  liquids. 
If  the  muscle  be  put  into  a  pure  NaCl  or  NaBr  solution 
of  the  same  osmotic  pressure  as  the  blood,  the  muscles 
contract  rhythmically  (4).  Yet  these  muscles  contain 
no  ganglion-cells.  Hence  it  is  not  the  presence  or  absence 
of  ganglion  -  cells  which  determines  the  spontaneous 
rhythmical  contractions,  but  the  presence  or  absence  of 
certai7i  ions,  Na  ions  start  or  increase  the  rate  of 
spontaneous  rhyth^nical  contractions  ;  Ca  ions  diminish 
the  rate  or  inhibit  such  contractions  altogether.  How 
can  these  ions  have  such  an  influence?  In  order  to 
explain  this  we  must  go  back  to  the  fundamental 
character     of    protoplasmic    motion.       Protoplasmic 


Fig.  3.  Experiment  in  Divid- 
ing A  Hydromedusa. 

The  amputated  margin  continues 
to  contract  rhythmically,  while 
the  bell  no  longer  contracts. 


20    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

motions  are  due  to  changes  in  the  physical  character 
of  the  colloidal  material  in  the  protoplasm.  These 
changes  may  consist  in  changes  in  the  state  of  matter 
or  in  the  absorption  of  water  by  these  colloids,  or  in 
secondary  changes  derived  from  those  before  men- 
tioned. We  know  that  the  physical  qualities  of  the 
colloids  are  influenced  greatly  by  the  nature  and 
osmotic  pressure  of  the  ions  in  the  surrounding  solu- 
tion. For  that  labile  equilibrium  of  the  colloids 
which  is  required  for  spontaneous  rhythmical  contrac- 
tions, the  Na,  Ca,  and  K  ions  must  be  present  in 
definite  proportions  in  the  tissues.  This  proportion 
must  be  different  for  the  centre  and  the  margin  of  a 
Hydromedusa.  While  for  the  margin  the  proportion 
in  which  these  three  ions  exist  in  the  sea-water  is 
adequate,  for  the  centre  of  a  Hydromedusa  more 
Na  ions  and  less  Ca  ions  are  required.  Hence,  if  we 
put  a  centre  without  the  margin  into  normal  sea-water 
it  does  not  beat,  but  it  will  beat  when  put  into  a  pure 
NaCl  or  NaBr  solution  of  the  same  osmotic  pressure 
as  sea-water.  In  the  pure  NaCl  solution  Na  ions  of 
the  solution  will  enter  into  the  tissues  and  take  the 
place  of  some  of  the  Ca  ions.  This  will  give  the  col- 
loids of  the  muscles  those  qualities  which  allow  rhyth- 
mical contractions.  If  too  many  Na  ions  enter  the 
tissues  of  the  centre  it  will  lose  its  irritability.  The 
latter  will,  in  this  case,  be  restored  again  by  adding  a 
trace  of  CaCl^  to  the  solution.  It  thus  happens  that 
the  problem  of  spontaneous  activity  is  no  longer  a 
question  of  the  presence  or  absence  of  the  ganglion- 


EXPERIMENTS  ON  MEDUSA 


21 


cells,  but  of  the  physical  qualities  of  the  colloidal  sub- 
stances in  the  tissues.  But  must  we  conclude  from 
this  that  the  Na  ions  are  the  cause  of  the  spontaneous 
rhythmical  contractions  of  the  Medusa?  I  think 
not.     The  ions  only  bring  about  a  certain  labile  equi- 


V^J^ff^^7f,/f^/JJJ?/J^?}JJ/77^f 


Ir 


v/y/^//y///////?W//f////mf/,jju>)>nj,>,,,i,jjji^jj,,j^j^,,,„„,,,,,fJ^^ 


Fig.  4.    Arrangement  for  Producing  Automatically  Pulsating 
Air-Bubbles.     (See  text.) 

librium  in  the  condition  of  the  colloids  of  the  con- 
tractile tissue  which  allows  the  true  cause  of  the 
contractions  to  be  effective.  But  what  is  this 
cause  ? 

J.  Rosenthal  seems  to  have  been  the  first  to  call 
attention  to  the  fact  that  it  is  in  no  way  essential  for 
a  rhythmical  phenomenon  to  have  a  rhythmical  cause, 
and  that  constant  conditions  can  lead  to  rhythmical 
effects.  If  a  small,  constant  stream  of  water  flows 
into  a  pipette,  it  will  pass  out  rhythmically  in  drops. 
The  weight  of  the  drop   must  be  greater  than  the 


22    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

surface-tension  in  the  periphery  of  the  opening  of  the 
outlet  before  the  drop  can  break  off.  As  long  as  the 
quantity  of  water  running  into  the  pipette,  in  the  unit 
of  time,  remains  below  a  certain  limit,  it  will  be  some 
time  before  the  drop  will  be  heavy  enough  to  fall. 
Quincke  has  given  a  simple  and  elegant  method  by 
which  it  is  easy  to  produce  rhythmical  contractions  in 
air  bubbles  (5).  I  will  describe  the  experiment  as  shown 
in  my  lectures.  A  glass  plate  P  (Fig.  4)  is  placed  in 
a  dish  B,  filled  with  water.  The  lower,  narrow  end  of 
the  thermometer  tube  T  is  under  and  at  the  middle 
of  the  air-bubble,  while  the  upper  end  rests  in  a  dish 
A  filled  with  95  per  cent,  alcohol.  The  alcohol 
rises  in  a  fine  stream  toward  the  centre  of  the  bubble. 
As  soon  as  the  alcohol  comes  in  contact  with  the 
bubble,  the  alcohol  spreads  out  on  the  limit  between 
the  air  and  the  water,  because  the  sum  of  the  surface- 
tensions  between  air  and  alcohol  and  alcohol  and 
water  is  less  than  the  surface-tension  between  air  and 
water.  By  the  decrease  in  the  surface-tension  the 
bubble  becomes  flatter  and  broader.  In  consequence 
of  the  vortex  movements  in  the  water  that  are  pro- 
duced by  the  spreading,  the  flow  of  the  alcohol  to  the 
bubble  is  interrupted.  The  layer  of  alcohol  around 
the  bubble  diffuses  rapidly  into  the  surrounding  water, 
and  the  bubble  becomes  again  higher  and  narrower. 
The  alcohol  can  flow  to  the  bubble  again  now  that 
the  vortex-movements  have  ceased,  and  the  flattening 
of  the  bubble  again  takes  place,  and  so  on.  Under 
the    above-mentioned    conditions    I    obtained   about 


EXPERIMENTS  ON  MEDUSA  23 

eighty  pulsations  per  minute  —  /.  e.,  about  the  period- 
icity of  the  heart. 

Now,  as  regards  the  origin  of  the  rhythmical  activ- 
ity of  Medusae,  of  the  heart,  and  of  respiratory  activity, 
we  can  imagine  that  a  constant  fermentative  produc- 
tion of  certain  compounds  in  the  automatically  active 
cell  corresponds  to  the  constant  flow  of  alcohol  in 
Quincke's  experiment.  These  substances  may  be  of 
such  a  nature  that  they  occasion  spreading-phenomena 
or  some  other  physical  change  in  the  colloids  of  the 
muscle.  But  a  certain  quantity  of  these  substances 
must  be  present  before  this  change  occurs,  hence  the 
periodicity  of  the  contractions.  But  whether  it  be  a 
constant  fermentative  production  of  some  substance 
or  not,  the  ultimate  constant  cause  for  the  production 
is  the  heat  or  the  intensity  factor  of  the  same  —  the 
temperature.  It  now  can  no  longer  surprise  us  that 
Romanes  found  that  the  centre  of  an  Acalepha  is  able 
to  beat  rhythmically  in  normal  sea-water  if  severed 
from  the  margin.  As  long  as  we  assume  that  the 
ganglion-cells  are  the  essential  element  in  spontaneity, 
this  experience  on  Acalephse  would  be  difficult  to  ex- 
plain. As  it  is,  we  are  only  obliged  to  conclude  that 
in  Acalephae  there  is  less  difference  between  the  col- 
loidal substances  of  the  margin  and  centre  than  in 
Hydromedusae. 

2.  Not  only  the  spontaneous  character  of  locomo- 
tions is  commonly  considered  to  be  due  to  ganglion- 
cells,  but  the  coordinated  character  of  these  motions 
as  well.     Let  us  see  how  far  this  notion  is  correct. 


24  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

Romanes  found  that  if  the  whole  margin  of  the 
umbrella  of  a  Hydromedusa  be  cut  off,  and  only  a  tiny 
piece  left,  this  is  sufficient  to  keep  up  the  spontane- 
ous activity  of  the  jelly-fish  in  sea-water.  From  this 
it  would  appear  that  any  element  of  the  margin  may 
be  considered  a  centre  for  the  rhythmical  contractions 
of  the  whole  Medusa.  But  if  this  be  the  case,  how 
does  it  happen  that  the  whole  umbrella  contracts  sim- 
ultaneously, and  why  do  we  not  find  one  part  of  the 
margin  in  systole  and  the  other  in  diastole  ?  This 
coordination  is  by  no  means  to  be  taken  for  granted. 
It  is  present  only  in  healthy  specimens,  and  is  wanting 
in  injured  or  dying  specimens,  a  fact  to  which  Roma- 
nes called  attention.  The  problem  of  the  mechanism 
of  this  coordination  has  been  dismissed  by  many  au- 
thors by  the  assumption  of  a  "  coordinating  centre  " 
that  is  supposed  to  control  this  coordination.  We 
shall  shortly  be  in  a  position  to  decide  whether  coor- 
dination in  lower  animals  is  controlled  by  a  special 
**  centre  of  coordination,"  or  whether  it  is  not  rather 
the  result  of  simple  laws  of  stimulation  and  conduction. 

Romanes  found  in  Acalephae  that  coordination 
ceases  when  all  direct  connection  between  the  nervous 
centres  has  been  interrupted  by  radial  incisions  in  the 
umbrella,  the  various  sectors  no  longer  contracting 
simultaneously.  The  same  thing  results  in  Hydrome- 
dusse,  if  conduction  through  the  nerve-ring  is  inter- 
rupted. In  such  cases,  the  radial  incision  must  reach 
well  toward  the  centre  of  the  bell.  If,  however,  such 
incisions  are  made  in  the  umbrella  without  injuring 


EXPERIMENTS  ON  MEDUSJE 


25 


the  margin  and  the  nerve-ring,  no  disturbance  of 
coordination  ensues.  It  seems  that  the  continuity  of 
the  structures  located  in  the  marginal  portions  of  the 
umbrella  is  necessary  for  the  coordinated  activity. 
Now  how  does  it  happen  that  so  long  as  the  continuity 
is  preserved  all  the  elements  act  synchronically,  while 
the  synchronism  disappears  if  the  continuity  is  inter- 
rupted?^ In  order  to  answer  this  question,  we  must 
turn  our  attention  to  an  organ  which  shows  the  phe- 
nomena of  coordinated  rhythmical  activity  in  a  strik- 
ing manner — namely,  the  heart.  If  the  heart  of  a  frog 
be  divided  into  several  pieces,  they  will  all  be  rhythm- 
ically active,  but  the  number  of  contractions  will  vary 
in  the  different  pieces.  The  sinus  venosus  beats  most 
rapidly,  and  the  number  of  its  contractions  in  a  unit 
of  time  equals  that  of  the  heart  before  it  was  divided. 
Thus  we  see  that  the  whole  heart  beats  in  the  rhythm 
of  the  part  that  has  the  maximum  nuTuber  of  contrac- 
tions per  m^inute.  From  this  we  must  assume  that  the 
coordination  of  the  heart's  activity  is  due  to  the  fact 
that  the  part  which  contracts  most  frequently,  forces 
the  other  parts  to  contract  in  the  same  rhythm.  They 
will  be  forced  to  do  this  if  the  activity  of  the  sinus 
venosus  acts  as  a  stimulus  upon  the  other  parts.  A 
centre  of  coordination  is  therefore  entirely  unneces- 
sary. 

Porter  succeeded  by  an  ingenious  method  in  causing 

'  It  should  be  emphasised  that  incisions  through  the  margin  alone  do  not 
interfere  with  coSrdination  in  Gonionemus,  but  that  it  is  necessary  to  continue 
the  incisions  to  the  centre  of  the  swimming-bell.  But  even  under  such  circum- 
stances the  animal  may  still  contract  in  a  coordinated  way. 


k 


26  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

strips  of  a  mammalian  heart  to  beat.  He  also  draws 
from  his  observations  the  conclusion  that  there 
is  no  reason  for  assuming  the  existence  of  a  centre  of 
a  coordination  (6).  In  Medusae,  also,  a  synchronical 
contraction  of  all  the  parts  takes  place  if  the  stimulus 
from  the  portion  first  active  can  travel  rapidly  enough 
to  the  rest  of  the  margin.  This  is  only  possible  when 
the  margin  is  uninjured.  It  is  evident,  however,  that 
the  neighbouring  tissue  as  well  as  the  nerve-ring  is  in- 
volved, because  the  radial  incision  must  reach  well 
toward  the  centre  of  the  bell  if  we  wish  to  stop  the 
coordination.  In  this  case  the  wave  of  stimulation 
must  pass  around  the  incisions,  a  process  which  in- 
volves so  much  time  that  the  separate  parts  are  able 
to  contract  independently,  and  the  synchronism  is 
lost.  In  injured  or  dying  Medusae,  where  the  contact 
of  the  cells  is  less  close,  uncoordinated,  rhythmical 
activity  occurs. 

In  order  to  test  this  idea  further,  I  proposed  to 
Dr.  Hargitt,  who  was  w^orking  in  my  laboratory,  that 
he  attempt  to  graft  two  Hydromedusae,  and  observe 
whether  they  continue  to  contract  synchronically  or 
independently  after  healing.  For  this  purpose  it  was 
necessary  to  remove  the  margin  of  the  Medusae. 
Two  of  them  were  then  placed  with  their  wounded 
surfaces  in  contact,  and  kept  in  this  position.  Figure 
5  shows  two  Gonionemi  grafted  in  this  way.  They 
grew  together  along  the  entire  line  of  contact  with  the 
exception  of  a  small  part  at  O.  New  tentacles  would 
probably  have  developed  there  in  time  had  we  not 


EXPERIMENTS  ON  MEDUSA 


27 


killed  the  animals  in  order  to  preserve  them.  In 
other  experiments,  the  two  animals  did  not  heal 
together  so  completely.  It  happened  in  the  case 
where  the  animals  had  grown 
together  most  completely,  as 
represented  in  Figure  5,  that 
they  contracted  synchronically 
like  one  animal  two  days  after 
the  operation.  The  animals, 
on  the  other  hand,  that  had  not 
grown  together  to  such  an  ex- 
tent did  not  contract  synchro- 
nically. I  believe  that  if  one 
could  succeed  in  healing  two 
hearts  together  completely, 
they  would  also  beat  synchro- 
nically. 

The  assumption  of  a  **  centre 
of  coordination "  situated  in 
the  ganglia  of  the  margin  of  a 
Medusa  thus  becomes  un- 
necessary.    In  the  frog's  heart, 

the  sinus  venosus  beats  faster  than  the  auricle,  ven- 
tricle, and  bulbus  aortae.  Hence,  each  contraction  of 
the  sinus  venosus  acts  as  a  stimulus,  which  causes  a 
contraction  of  the  auricles,  and  the  contraction  of  the 
latter  is  the  stimulus  which  causes  the  contraction  of 
the  ventricle  and  bulbus  aortae.  It  would  follow  from 
this  that  if  we  could  cause  the  bulbus  aortae  in  the 
frog's  heart  to  beat  as  fast  as  the  sinus  venosus  we 


Fig.  5. 


Dr.   Hargitt's  Ex- 
periment. 


Two  Gonionemi  grafted  to- 
gether. Two  days  after  the 
operation  synchronous  con- 
tractions of  both  animals 
were  observed. 


28  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 


might  see  a  reversal  of  the  heart-beat.  Nature  has 
made  this  experiment  for  us  on  a  large  scale  in  the 
Ascidian's  heart  (Fig.  6). 

The  latter  has  the   peculiarity  that  the  waves  of 

contraction  do  not 
spread  out  con- 
stantly in  one  di- 
rection, as  in  the 
hearts  of  other  an- 
imals,  but   perist- 

^     ^    _^  ^  „  altic  and  antiperi- 

FiG.  6.    Diagram  of  the  Ascidian  Heart.  .  ^ 

T  .v    A    J-    u   _      .    .•  r      .•      staltic  waves  of 

In  the  Ascidian  heart,  contractions  occur  for  a  time 

in  the  direction  from  a  to  b,  and  then  from  b  to  Contraction     alter- 

a.     If  the  heart  be  cut  open  at  c,  the  left  half  nate  in  it        If    for 
contracts  only  in  the  direction  from  a  to  f ,  the  ,  .       , 

right  half  only  in  the  direction  from  b  \.o  c.  example,     it    haS 

contracted  five 
hundred  times  in  succession  from  left  to  right,  sending 
the  blood  to  the  right,  this  activity  is  followed  by  per- 
haps three  hundred  pulsations  from  right  to  left, 
which  cause  the  blood  to  flow  through  the  blood- 
vessels in  the  opposite  direction.  These  contractions 
are  followed  again  by  a  large  number  of  pulsations 
from  left  to  right,  etc.  Mr.  Lingle  made  the  follow- 
ing experiments  on  the  Ascidian's  heart  at  Wood's 
Holl  in  1892.  \{  a  b  (Fig.  6)  be  an  Ascidian's  heart 
and  it  be  divided  at  ^,  both  pieces,  a  c^  and  b  c,  con- 
tract uninterruptedly  in  a  constant  direction,  the 
former  in  the  direction  from  a  to  c,  and  the  latter  in 
the  direction  from  b  to  c.  Mr.  Lingle  found,  further- 
more, that  the  source  of  the  automatic  activity  is 


EXPERIMENTS  ON  MEDUSA  29 

confined  to  two  small  regions  {a  and  b,  Fig.  6)  which 
correspond  to  the  sinus  venosus  and  the  bulbus  aortae 
of  the  frog's  heart.  When  we  excise  these  two  pieces 
from  the  heart  they  continue  to  beat  without  inter- 
ruption, while  the  long  part  between  the  two  pieces 
no  longer  pulsates  (in  sea-water  at  least).  These  ex- 
periments, it  seems  to  me,  leave  no  room  for  doubt 
that  the  change  in  the  direction  of  the  contraction  in 
the  Ascidian's  heart  is  determined  by  each  of  the  two 
ends  getting  the  upper  hand  alternately,  and  forcing 
the  other  centre  to  act  in  its  rhythm  for  a  time.  This 
*'  getting  the  upper  hand  "  might  possibly  mean  no- 
thing more  than  that  one  end  gains  the  time  in  which 
to  send  off  a  wave  of  contraction  before  the  other 
end  begins  to  contract.  For  this  it  is  only  necessary 
that  a  single  heart-beat  of  the  leading  end  be  delayed 
or  fail  entirely,  a  phenomenon  that  also  appears  oc- 
casionally in  the  human  heart.  In  this  way  the  other 
end  of  the  heart  gains  time  in  which  to  send  out  a 
wave  of  contraction,  and  its  automatic  activity  will 
continue  to  be  the  stimulus  for  the  activity  of  the 
first  end  until  a  delay  occurs  in  one  beat  or  until  one 
beat  is  skipped,  thus  allowing  the  first  end  time  again 
to  become  automatically  active,  and  so  on. 

Last  year  I  asked  the  members  of  the  class  in  gen- 
eral physiology  at  Wood's  Holl  to  find  out  whether 
the  latter  view  was  correct.  Their  observations  were 
as  follows  :  Suppose  at  a  certain  time  a  to  be  the 
active  and  b  the  passive  end  of  the  heart.  After  a 
short  time  a  begins  to  beat  more  slowly  or  ceases  to 


30  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

beat  altogether.  During  the  pause,  the  end  b  suc- 
ceeds in  sending  out  a  wave  of  contraction  which 
reaches  a  before  it  has  had  time  to  send  out  a  wave 
of  its  own.  One  sees  occasionally  at  the  time  of  a 
reversal  that  at  first  both  ends  send  out  contraction- 
waves  which  may  meet  in  the  middle  of  the  heart. 
At  the  next  heart-beat,  the  end  which  is  about  to  stop 
delays  the  sending  out  of  the  wave  a  little  more,  and 
at  the  next  heart-beat  the  wave  starting  from  the 
other  end  can  pass  over  the  whole  heart  without  being 
blocked. 

Hence  the  coordination  of  movements  In  Medusae 
(or  in  the  heart)  is  not  due  to  a  hypothetical  centre 
of  coordination  situated  in  the  ganglion-cells,  but  to 
the  fact  that  the  element  which  is  first  active  acts 
as  a  stimulus  upon  its  next  element,  and  so  on. 

3.  It  may  be  shown  that  even  more  specialised 
forms  of  coordination  do  not  depend  upon  the  pre- 
sence or  interference  of  ganglia.  When  the  back  of 
a  frog  Is  touched  with  acetic  acid,  the  frog  wipes  off 
the  acid  with  Its  foot.  If  one  leg  Is  tied.  It  uses  the 
other  for  this  purpose.  The  turtle  acts  in  a  similar 
manner  when  acetic  acid  is  applied  to  the  back  of  its 
shell.  It  cannot  reach  the  stimulated  spot,  but  the 
legs  move  dorsally  under  the  shell  as  far  as  possible 
towards  it.  Physiology  has  contented  Itself  In  regard 
to  these  phenomena  by  pointing  to  the  complicated 
nature  and  Impenetrable  structural  secrets  of  the 
central  nervous  system.  Yet  the  same  reactions  oc- 
cur  In    a    Hydromedusa,    in   which    case   the   term 


EXPERIMENTS  ON  MEDUSAE  31 

*' central  nervous  system"  has  only  a  conventional 
significance.  Romanes  found  that  if  we  stimulate  a 
spot  a  (Fig.  7)  on  the  concave  side  of  the  umbrella 
of  a  Tiaropsis  indicans  with  a  needle,  the  manubrium 

is  broug^ht  to  the  

stimulated   spot  y^  ^\^     ..••' 

(Fig.  7),  as  though        /    ^^  -^ 

the  animal  wished      /    /^    |  \ 

to    remove    the     /  /  I       f        \      I 

stimulating  object    /  /  \     \         \     / 

(2).     This   move-   (/L^s:^====^^^^^^v?^     1/ 

ment  takes  place   1^^^-^^^  ^^3f' 

as  follows:    A  "'''''liil^^ 

bending  of    the 

m  a  n  u  b  r  i  u  m  as  Tr  ,v       •  .  *u  •    •     .•     1  *  ^  *a. 

If  the  point  a  on  the  margin  is  stimulated,  the 
well  as  01  the  bell  manubrium  is  brought  to  the  stimulated  spot, 
ensues  in  that  mer-  somewhat  as  a  decapitated  frog  tries  to  wipe  off 
...  ft  *  ^op  of  acetic  acid  with  its  foot. 

idian  of  the  um- 
brella which  passes  through  the  stimulated  point  a. 
It  seems  as  though  all  the  muscle-fibres  cooperated 
in  bringing  the  manubrium  to  the  stimulated  spot. 
The  central  nervous  system  has  nothing  to  do  with 
this  reaction,  for  Romanes  found  that  it  continued 
after  excision  of  the  whole  margin  with  the  nerve- 
ring.  On  the  other  hand,  if  we  make  an  incision 
in  the  umbrella  parallel  to  the  margin  and  stimulate 
a  spot  below  the  line  of  incision,  movements  of 
the  manubrium,  although  not  pronounced  ones,  ap- 
pear in  the  direction  of  the  quadrant  where  the 
stimulated  spot  is  located,  but  an  exact  localisation 


Fig.  7.    Localising  Reflex  in  Tiaropsis 
Indicans. 


32  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 


Fig.  8.  Diagram  for  Explain- 
ing THE  Localising  Reflex  in 
Medusae.     (See  text.) 


is  impossible.  Romanes  concludes  from  this  that 
there  are  radial  lines  of  differentiated  tissue  pass- 
ing through  all  parts  of  the  bell  and  that  it  is 
their  function  to  transmit  impressions  to  the  manu- 
brium. He  assumes  that 
this  tissue  is  of  a  nervous 
character.  I  believe  that 
the  whole  phenomenon  can 
be  explained  without  the  as- 
sumption of  a  special  differ- 
entiation of  nervous  tissue 
in  radial  directions.  It  seems 
to  me  that  the  following  as- 
sumption is  possible :  Every  localised  stimulus  leads 
to  an  increase  in  the  muscular  tension  on  all  sides, 
which  is  most  intense  near  the  stimulated  spot.  Now 
if  we  decompose  each  of  the  lines  of  increase  of  tension 
{aa'  ab'  ad  ad'  ae\  Fig.  8)  radiating  from  the  stimul- 
ated spot,  into  a  meridional  component  aa'  dd'  bb\  etc., 
and  an  equatorial  component,  it  is  evident  that  the  lat- 
ter can  have  no  influence  on  the  manubrium.  Only 
the  meridional  components  can  have  an  influence,  and 
of  these  the  one  passing  through  the  stimulated  spot  is 
the  largest.  This  fact  must  necessarily  cause  a  bend- 
ing of  the  manubrium  toward  the  stimulated  spot. 
It  also  shows  why  an  incision  parallel  to  the  mar- 
gin of  the  umbrella  makes  an  exact  localisation  impos- 
sible and  only  allows  uncertain  movements  towards 
the  stimulated  quadrant. 

I    hardly   believe    that    the    mechanisms    for   the 


EXPERMIENTS  ON  MEDUSA  33 

analogous  reflex  in  a  frog  or  turtle  are  of  a  more  com- 
plicated character.  Nature  works  with  very  simple 
tools.  The  tool  employed  in  the  reflex  of  localisa- 
tion is  the  curvature  produced  by  stimulation, —  con- 
tact, for  instance.  We  meet  with  this  in  its  simplest 
form  in  plants,  in  which  the  side  that  comes  in  con- 
tact with  a  solid  body  becomes  concave.  Plants  cer- 
tainly possess  no  central  nervous  system  containing 
mysterious  reflex  structures.  In  their  case,  irritabil- 
ity and  conductibility  suffice  as  an  explanation.  In 
Medusae  the  method  appears  more  complicated  only 
in  so  far  as  in  them  the  contractile  tissue  is  real  mus- 
cle-fibre. .  In  the  frog,  the  only  further  complication 
is  the  fact  that  the  conduction  takes  place  through  a 
special  kind  of  tissue — namely,  nerve-tissue.  In  its 
first  anlage,  this  central  nervous  system  is  of  a  very 
simple  segmental  character.  I  believe  that  the  cent- 
ral nervous  system  preserves  this  simple  character 
better  than  any  other  tissue.  The  muscles  undergo 
considerable  displacement  during  the  development, 
but  the  changes  occurring  in  the  central  nervous  sys- 
^tem  by  no  means  equal  those  occurring  in  the  mus- 
clar system. 

It  seems  thus  possible  to  explain  the  above-men- 

:ioned  phenomena    of  coordination    in    Medusae  by 

leans  of  the  simple  facts  of  irritability  and  conduct- 

[ivity  without  attributing  any  other  functions  to  the 

;anglion-cell  except  those  which  occur  in  all  conduct- 

[ing  protoplasm. 


34 


COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 


Bibliography 


1.  O,  u.  R.  Hertwig.  Das  Nervensystem  und  die  Sinnesorgane 
der  Medusen. 

2.  Romanes,  G.  J.  Jellyfish^  Starfish  and  Sea  Urchins. 
The  International  Science  Series,  1893. 

3.  LoEB,  J.  On  the  Different  Effects  of  Ions  upon  Myogenic  and 
Neurogenic  Rhythmical  Contractions^  etc.,  American  Journal  of 
Physiology^  vol.  iii.,  1900. 

4.  LoEB,  J.  Ueber  lonen,  welche  rhythmische  Zuckungen  der 
Skelettmuskeln  hervorrufen.  Festschrift  fur  Fick.  Braunschweig, 
1899. 

5.  Quincke.  Ueder  periodische  Ausbreitung  an  Fliissigkeits- 
oberfldchen^  etc.  Sitzungsberichte  der  Berliner  Akademie  der  Wis- 
sensch.y    1888,  ii.,  S.  791. 

6.  Porter,  W.  T.  The  Coordination  of  the  Ventricle,  The 
American  Journal  of  Physiology ^  vol.  ii.,  1899. 


CHAPTER  III 

THE  CENTRAL  NERVOUS  SYSTEM  OF  ASCIDIANS 
AND  ITS  SIGNIFICANCE  IN  THE  MECHANISM 
OF  REFLEXES 

I.  If  we  wished  to  observe  the  order  of  the  natural 
system  in  this  book,  we  should  not  let  the  Ascidians 
follow  the  Medusae.  We  consider  it  more  profitable, 
however,  to  discuss  simple  cases  before  taking  up  the 
more  complicated  ones.  Having  reached  the  con- 
clusion, at  the  end  of  the  preceding  chapter,  that  the 
spontaneous  coordinated  activities  in  Medusae  are  not 
due  to  specific  morphological  structures  of  the  gan- 
glion-cells, we  will  now  attempt  to  find  out  whether 
the  reflex  actions  of  animals  depend  upon  the  struct- 
ure of  the  central  nervous  system  or  of  the  peripheral 
parts.  In  Ascidians  the  central  nervous  system  con- 
sists of  a  single  ganglion  {d,  Fig.  9).  This  ganglion 
is  situated  between  the  oral  and  aboral  tubes  {a  and 
b,  Fig.  9). 

Ciona  intestinalis  (Fig.  9),  a  large,  transparent 
Ascidian,  possesses  a  very  characteristic  reflex.  If 
either  the  oral  or  aboral  opening  be  touched,  both 
openings  close,  and  the  whole  animal  contracts   so 

35 


^6    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 


that  it  becomes  small  and  round.  This  reflex  is  de- 
termined by  two  groups  of  muscles,  first  by  ring- 
muscles  in  the  oral  and  aboral  openings,  second  by 

longitudinal  muscles, 
which  run  lengthwise 
through  the  animal.  By 
the  contraction  of  these 
muscles  the  animal  is 
protected  from  the  en- 
trance of  foreign  bodies 
into  the  body  cavity. 
This  reaction  is  a  typ- 
ical reflex  act,  and  is 
eminently  purposeful. 
According  to  the  pre- 
vailing ideas  concern- 
ing the  decisive  role 
that  the  ganglion  plays 
in  reflexes,  the  pro- 
cedure is  as  follows  : 
If  the  oral  or  aboral 
opening  be  touched,  the  stimulation  is  conducted 
through  the  peripheral  nerves  to  the  ganglion,  where 
a  mysterious  reflex  mechanism  is  brought  into  play, 
which  gives  the  muscles  the  command  to  contract  in 
a  manner  corresponding  to  the  nature  of  the  stimulus. 
Ferrier,  for  instance,  in  his  text-book,  mentions  the 
one  ganglion  of  the  Ascidians  as  illustrative  of  the 
significance  of  the  ganglion  in  reflexes. 

I  removed  the  ganglion  from  a  number  of  Cionse. 


Fig.  9.     CioNA  Intestinalis. 

n  oral,  b  aboral  opening ;  r ,  foot,  d,  location  of 
ganglion. 


EXPERIMENTS  ON  ASCIDIANS  37 

For  some  time  after  the  operation,  in  most  cases  for 
about  twenty-four  hours,  the  animals  remained  con- 
tracted. At  the  end  of  this  period  they  began  to  re- 
lax again.  To  my  great  surprise,  I  found  that  the 
typical  reflex  continued.  If  we  let  a  drop  of  water 
fall  on  such  an  animal,  the  typical  reflex  act  is  pro- 
duced just  as  in  the  normal  animal.  Hence  the  reflex 
cannot  be  determined  by  specific  structures  of  the 
ganglion.  But  what  does  determine  the  reflexes,  and 
what  is  the  function  of  the  ganglion  ? 

The  answer  to  the  first  question  must  be  that  the 
reflex  is  determined  by  the  structure  and  arrange- 
ment of  the  peripheral  parts,  especially  the  muscles. 
The  mechanical  stimulus  throws  the  muscles  directly 
into  activity,  and  the  stimulation  is  transmitted  from 
muscle-element  to  muscle-element  directly,  as  in  the 
heart  or  the  ureter.  But  is  the  central  nervous  system 
superfluous  in  this  animal  ?  We  get  the  answer  to 
this  question  if  we  determine  the  threshold  of  stimul- 
ation. The  threshold  of  stimulation  for  producing 
this  reflex  is  higher  in  animals  which  have  been 
operated  upon  than  in  normal  animals.  As  the 
source  of  the  stimulus,  I  used  the  kinetic  energy  of 
drops  of  water,  which  fell  from  a  pipette  upon  the 
animal.  Since  the  weight  of  the  falling  drop  in  the 
pipette  is  always  the  same,  the  minimum  of  the  height 
from  which  a  falling  drop  can  produce  a  contraction  is 
a  convenient  measure  of  the  irritability ;  the  latter  is 
of  course  equal  to  the  reciprocal  value  of  the  thresh- 
old of  stimulation.     In  one  case  there  were  in  an 


38    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

aquarium  (equally  near  the  surface),  a  Ciona  freshly 
operated  upon  and  a  normal  Clona.  The  minimum 
height  from  which  a  contraction  could  be  produced 
was  as  follows  for  the  normal  animal  (a)  and  the 
animal  operated  upon  {b)  : 

a  (normal)  b  (operated) 

8  mm  65  mm 

4  mm  75  mm 

10  m.m  80  mm 

80  mm 
In   two   other   animals   used   for   the   experiment  I 
obtained  the  following  values  : 

a  (normal)  b  (operated) 

6  mm.  22  m.m. 

8  m^m  20  mm. 

It  seems  to  me  that  the  difference  in  the  irritability 
arises  from  the  fact  that  in  the  normal  Ascidian  the 
stimulation  is  conducted  through  the  nerves  and  the 
ganglion,  in  which  case  less  energy  is  required.  In 
the  Ascidian  operated  upon,  however,  the  muscles  are 
stimulated  directly,  and  the  conduction  of  the  stim- 
ulation probably  takes  place  from  muscle-cell  to 
muscle-cell,  just  as  in  the  heart.  We  know,  more- 
over, that  the  direct  irritability  of  muscle-fibres  is  not 
so  great  as  that  of  the  nerves.  Hence  the  nerves  and 
the  ganglion  only  play  the  part  of  a  more  sensitive  and 
quicker  conductor  for  the  stimulus  (i). 

2.   It  may  seem  as  though  no   conclusions   could 
be  drawn  from  these  cases  in  regard  to  the  ''  reflex 


I 


EXPERIMENTS  ON  ASCIDIANS  39 

centres  "  of  higher  animals.  It  is  frequently  stated 
that  in  higher  animals  the  ganglia  have  assumed  func- 
tions which  in  lower  animals  can  be  performed  by  the 
peripheral  organs.  It  is  similarly  stated  that  the  higher 
the  animal  ranks  in  the  natural  system,  the  more  the 
functions  ''migrate"  toward  the  cerebral  hemispheres. 
But  how  such  an  upward  migration  of  functions  is 
conceivable,  none  of  these  authors  attempt  to  explain. 
It  can  easily  be  shown,  however,  that  conditions  are 
the  same  in  higher  and  lower  animals.  We  must  only 
be  careful  to  homologise  a  lower  form  with  a  single 
organ  or  segment  of  a  higher  animal.  When  the  in- 
tensity of  the  light  is  suddenly  increased,  the  pupil  of 
our  eye  becomes  narrower.  The  sphincter  of  the  iris 
contracts,  and  the  rays  of  light  are  excluded  just  as 
foreign  bodies  are  shut  out  by  the  contraction  of  the 
sphincters  in  the  Ascidians.  In  the  eye,  just  as  in  the 
Ascidian,  we  have  to  deal  with  a  typical  reflex  act. 
The  increased  intensity  of  the  light  stimulates  the 
retina.  The  stimulation  passes  through  the  optic 
nerve  to  its  centres,  and  is  carried  from  there  by 
means  of  the  oculomotorius  nerve  to  the  sphincter  of 
the  iris,  which  contracts.  It  would  nevertheless  be 
wrong  to  assume  that  the  centre  for  the  pupillary 
reflex  plays  any  other  part  in  this  process  than  that  of 
a  protoplasmic  connection  between  the  retina  and  the 
iris.  It  has  been  shown  by  Arnold,  and  later  by 
Brown-Sequard  and  Budge,  that  even  in  the  excised 
iris  the  pupil  still  contracts  when  the  light  strikes  the 
former.     I    myself   have    often    observed    in  sharks, 


40    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

whose  brain  I  had  removed,  that  Hght  caused  the 
pupil  to  contract  several  hours  after  death,  when 
signs  of  decomposition  had  already  begun  to  appear. 
Steinach  has  proved  that  in  this  case  the  muscle- 
elements  in  the  iris  are  stimulated  directly  by  the  light 
(3).  This  reflex  is  therefore  determined  by  the  mus- 
cles of  the  iris,  and  the  nervous  connections  serve 
only  as  quicker  and  more  sensitive  conductors.  Thus 
we  see  that  the  eyeball  behaves  toward  light  just  as 
the  Ascidian  behaves  toward  mechanical  stimuli. 

Some  physiologists  seem  to  doubt  that  the  muscles 
can  be  stimulated  directly  by  light  without  the  inter- 
vention of  the  ganglion-cells.  But  we  know  that 
phenomena  of  contraction  are  also  produced  by  the 
light  in  the  unicellular  swarmspores  of  algae,  which 
certainly  contain  no  ganglia.  Furthermore,  no  one 
doubts  that  muscles  without  ganglion-cells  can  also  be 
stimulated  chemically  or  mechanically.  Why  should 
there  not  also  be  muscle-fibres  that  can  be  stimulated 
directly  by  light  ?  There  is  no  reason  for  assuming 
that  all  muscles  must  behave  exactly  like  the  muscles 
of  the  frog's  leg,  simply  because  the  experiments  on 
it  have  by  chance  furnished  the  prevailing  views  con- 
cerning muscles. 

The  reader  may  believe  that  the  pupillary  reflex  is 
an  exceptional  case,  but  this  is  not  true.  Defaecation 
and  urination  in  higher  animals  may  be  considered  as 
reflex  phenomena  of  the  spinal  cord.  The  pressure  of 
the  faeces  or  of  the  urine  acts  as  a  stimulus,  which 
affects  the  centres  for  the  activity  of  the  muscles  of 


I 


EXPERIMENTS  ON  ASCIDIANS  41 

these  organs,  and  this  stimulation  is  said  to  cause  the 
contracted  sphincters  to  relax.  Goltz  and  Ewald 
have  found,  however,  that  after  extirpation  of  the  en- 
tire spinal  cord  up  to  the  cervical  part,  defaecation  and 
urination  still  occur  normally  (4).  Only  for  a  time  after 
the  operation  the  sphincters  are  relaxed.  Later  on 
everything  again  becomes  normal.  These  phenomena 
probably  belong  to  the  same  class  as  the  one  already 
described  in  the  Ascidian.  The  processes  in  the 
normal  evacuations  of  the  bladder  and  rectum  are  not 
determined  by  the  morphological  structure  of  the  so- 
called  reflex  centre,  but  by  the  muscles  of  the  bladder 
and  of  the  rectum  themselves.  The  spinal  cord 
serves  only  as  a  more  sensitive  and  quicker  conductor 
for  the  stimulus.  Goltz  and  Ewald  are  inclined,  it  is 
true,  to  assume  that,  after  all,  ganglion-cells  or  un- 
known nervous  structures  determine  these  results. 
But  the  fact  that  the  muscles  of  the  skeleton  can  be 
caused  to  contract  rhythmically  when  put  in  the  right 
solution,  makes  this  assumption  unnecessary ;  more- 
over, the  facts  of  comparative  physiology  must  also  be 
taken  into  consideration.  The  Actinia  mesembryan- 
themum  of  the  East  Sea  and  the  Mediterranean  per- 
haps show  fewer  differences  morphologically  than  the 
sphincter  ani  and  the  gastrocnemius,  and  yet  the 
Actinia  mesembryanthemum  of  the  Mediterranean 
shows  a  form  of  irritability  which  the  Actinian  of  the 
same  name  from  the  East  Sea  does  not  show,  namely, 
negative  geotropism.  I  mention  this  illustration,  to 
which  many  others  might  be  added,  in  order  to  show 


42    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

that  forms  which  are  morphologically  alike  need  not 
necessarily  be  alike  in  all  their  reactions.  Experiments 
on  fermentation  show  that  a  small  stereochemical  dif- 
ference of  a  carbohydrate  or  proteid  can  produce  an 
entirely  different  physiological  effect. 

The  possibility,  of  course,  remains  that  scattered 
ganglion-cells  exist  in  Ascidians  under  the  epidermis 
just  as  in  Medusae.  Mr.  Hunter,  who  has  studied  the 
nervous  system  of  Ascidians,  informs  us  that  he  has 
found  cells  in  certain  places  under  the  epidermis  of  As- 
cidians which  he  believes  to  be  ganglion-cells.  But 
after  all  that  has  been  said  about  the  scattered  gan- 
glion-cells in  Hydromedusae  (see  page  19)  and  their 
role  in  rhythmical  contractions,  it  is  not  necessary  to 
consider  the  importance  of  scattered  ganglion-cells  for 
reflexes.  Schaper  has  recently  made  an  observation 
which  makes  it  seem  as  though  in  the  young  larvae  of 
Amphibians  conditions  similar  to  those  in  Ascidians 
exist.  He  amputated  the  brain  of  the  larva  of  a  frog 
during  the  first  days  of  development,  and  saw  that  the 
animal  was  still  able  to  move  spontaneously  seven  days 
after  the  operation.  When  sections  of  the  animal  were 
made,  it  was  found  that  the  spinal  cord  had  also  per- 
ished (2).  This  observation  should  be  repeated  and 
enlarged  upon.  It  is  quite  possible  that  during  the 
first  days  of  development  a  direct  transmission  of  the 
waves  of  stimulation  may  take  place  from  the  skin  to 
the  muscles  in  the  larva  of  the  frog,  without  the  in- 
tervention of  the  central  nervous  system,  as  happens 
in  the  Ascidians. 


EXPERIMENTS  ON  ASCIDIANS  43 

3.  The  objection  might  now  be  raised  that  the 
bladder  and  rectum  are  minor  organs  of  the  body. 
But  what  has  been  said  above  concerning  them 
also  holds  good  for  larger  and  more  important 
groups  of  organs,  namely  for  the  blood-vessels. 
These  are  able  to  adapt  their  width  to  external  con- 
ditions ;  the  vessels  of  the  skin  become  dilated  when 
a  loss  of  heat  is  desirable,  and  they  contract  in  the 
cold  when  the  loss  of  heat  should  be  reduced.  It  is 
assumed  that  the  mechanisms  for  these  purposeful 
reflexes  are  contained  in  the  central  nervous  system. 
Goltz  and  Ewald  (4)  have  found,  however,  that  dogs 
which  have  lost  the  spinal  cord  almost  up  to  the  me- 
dulla oblongata  live  for  years.  This  alone  proves 
that  the  blood-vessels  can  adapt  themselves  to  the 
external  temperature,  independently  of  the  central 
nervous  system.  Goltz  had  already  proved  that  the 
blood-vessels  regain  their  tonus  if  all  the  nerves  of  a 
limb  be  severed,  the  limb  being  connected  with  the 
animal  only  by  means  of  the  blood-vessels.  The 
same  thing  occurs  after  extirpation  of  the  spinal  cord. 
The  temperature  of  the  hind-paws  of  animals  whose 
spinal  cord  has  been  destroyed  up  to  the  thoracic 
part  becomes  normal  again  after  the  operation — that 
IS  to  say,  the  hind-paws  have  the  same  temperature 
as  the  fore-paws  which  remain  connected  with  the 
central  nervous  system.  If  we  hold  the  hand  in 
snow  for  a  time,  we  observe  as  a  local  after-effect  a 
relaxation  of  the  muscles  of  the  blood-vessels  and  an 
increase  in  the  temperature  of  the  hand.     Goltz  and 


44    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

Ewald  were  able  to  show  that  the  same  phenomena 
may  also  be  observed  when  the  hind-legs  of  dogs 
whose  spinal  cord  has  been  destroyed  are  packed  for 
a  time  in  snow. 

From  the  standpoint  of  human  physiology  these 
results  seem  strange,  but  from  that  of  comparative 
physiology  they  are  readily  understood.  The  various 
reactions  of  plants  to  external  stimuli  are  just  as  pur- 
poseful as  those  of  animals.  Why  should  it  not  be 
possible,  then,  for  single  organs  and  tissues  of  higher 
animals  to  react  purposefully  to  external  stimuli,  and 
is  there  any  reason  why  the  purposeful  character  of  a 
reaction  should  be  dependent  upon  the  structure  of 
the  central  nervous  system  ? 

We  have  been  able  to  rid  ourselves  of  erroneous 
views  concerning  the  significance  of  the  ganglia  of 
the  central  nervous  system  in  higher  animals  through 
the  help  of  the  Ascidians  ;  they  also  help  us  further  to 
determine  the  true  role  of  the  nervous  system.  Al- 
though the  dogs  experimented  upon  by  Goltz  and 
Ewald  were  able  to  adapt  the  width  of  their  blood- 
vessels to  the  variations  of  temperature,  it  was  neces- 
sary to  shield  them  much  more  carefully  from  sudden 
changes  of  temperature  than  is  necessary  in  the  case 
of  normal  animals.  The  threshold  of  stimulation  was 
raised  and  probably  the  rapidity  of  the  conduction 
decreased.  For  this  reason,  dogs  whose  spinal  cord 
is  destroyed  are  no  longer  fit  to  live  out-of-doors. 
As  regards  regulation  of  temperature,  they  are  like 
an  intoxicated  person,  and  would  perish  in  the  cold 


EXPERIMENTS  ON  ASCIDIANS  45 

much  sooner  than  a  normal  animal.  Hence  the 
nervous  system  does  not  contain  any  regulating  me- 
chanisms, but  it  serves  as  a  quicker  conductor,  and 
allows  the  peripheral  organs  to  work  with  greater 
precision. 

4.  Bethe  has  recently  made  a  difficult  experiment 
on  Carcinus  mcBuas,  which,  however,  was  successful 
in  only  two  cases.  If  this  experiment  is  correct,  it 
proves  that,  in  the  conduction  of  a  reflex  in  the  cent- 
ral nervous  system,  the  process  of  conduction  does 
not  of  necessity  pass  through  the  ganglion-cell  itself 
(5).  An  anatomical  observation  caused  Bethe  to 
perforni  this  operation.  **  Almost  all  the  ganglion- 
cells  of  Carcinus  are  unipolar,  and  often  the  axis-cyl- 
inder of  the  cell  runs  for  a  long  distance  before  it 
gives  off  the  first  dendrites  and  sends  out  the  peri- 
pheral fibre.  It  seemed  very  strange  to  me  that  a 
stimulus  entering  through  the  sensory  nerves  into  the 
central  organ  should  go  through  the  dendrites  to  the 
far-distant  motor-ganglion  cells,  and  travel  the  great 
part  of  the  same  path  before  entering  the  peripheral 
motor  fibre,  instead  of  going  directly  to  the  motor 
fibre.  It  was  easy  to  decide  this  question  by  sep- 
arating the  ganglion-cells  with  their  axis-cylinder 
process  from  the  motor  neurons  without  injuring  the 
neuropiles.  If  the  ganglion-cell  were  absolutely  es- 
sential for  the  reflex,  the  muscles  involved  should 
become  paralysed  immediately  after  the  operation  ;  if 
it  were  not  essential,  no  paralysis  should  occur,  at  least 
for   some  time,  and  the  stimulus   could    go    across 


k 


46    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

directly  from  the  dendrites  to  the  peripheral  fibre."  It 
was  possible  to  perform  the  operation  in  Carcinus 
on  the  ganglion-cells  which  innervate  the  muscles  of 
the  second  antenna.  The  cutting  of  the  peripheral 
nerves  {Antennarius  secundus)  that  go  to  these  gan- 
glion-cells immediately  causes  a  complete  paralysis  of 
the  antennae,  a  proof  that  the  fibres  of  these  nerves 
are  the  only  conductors  of  the  stimulus  which  can 
call  forth  a  reflex  movement  of  these  antennae.  But 
when  Bethe  removed  the  ganglion-cells,  without  in- 
juring the  neuropile  of  the  second  antenna,  ''the 
second  antenna  retained  its  tonus  and  its  reflex  irrit- 
ability. It  does  not  hang  down  limp,  but  remains 
stiff  and  in  the  normal  position.  When  stimulated, 
it  is  withdrawn,  but  is  stretched  out  again  when  the 
stimulation  ceases.  From  this  it  is  evident  that  the 
ganglion-cells  are  not  necessary  for  reflexes.  The  re- 
flex arc  either  does  not  pass  through  the  ganglion- 
cells  or  does  not  need  to  pass  through  them.  It  is 
further  apparent  that  the  ganglion-cell  has  nothing  to 
do  with  the  tonus  of  the  muscles,  and  that  the  per- 
manent influence  which  the  central  nervous  system 
exercises  upon  the  tension  of  the  muscles  is  not  pro- 
duced in  the  ganglion-cells  (6)." 

This  experiment,  even  if  it  be  correct,  adds  no- 
thing of  importance  to  our  conclusions.  If  the  reflex 
arc  acts  only  as  a  quick  protoplasmic  conductor,  the 
question  whether  the  stimulus  has  to  pass  through  the 
ganglion  itself  or  not  becomes  of  secondary  import- 
ance. 


EXPERIMENTS  ON  ASCIDIANS  47 

Bibliography. 

1.  LoEB,  J.      Untersuchungen  zur  physiologischen  Morphologie 
der  Thiere.     II.     Wiirzburg,  1892,  S.  37. 

2.  ScHAPER,  A.     Experimentelle   Studien   an   Amphibienlarven. 
Archiv  fiir  Entwicklungsmechanik^  Bd.  vi.,  1898. 

3.  Steinach,  E.      Untersuchungen  zur  vergleichenden  Physiolo- 
gie  der  Iris,    Pfluger's  Archiv,  Bd.  lii.,  1892. 

4.  GoLTZ  und  Ewald.     Der  Hund  mit  verkUrztem  RUcken- 
mark.     Pflilgers  Arch.^  Bd.  Ixiii.,  1896. 

5.  Bethe,  a.      Das  Centralnervensystem  von  Carcinus  manas. 

I.  Theil,  II.      Mittheilung.     Archiv  f.  mikroskop.  Anatomie  und 
EntwicklungsgeschichtCy  Bd.  1.,  1897. 

6.  Bethe,  A.      Das  Centralnervensystem  von  Carcinus  mcenas. 

II.  Theil.      Arch.  f.   mikroskop.     Anatomie  und  Entwicklungs- 
geschichte,  Bd.  li.,  1898. 


CHAPTER    IV 

EXPERIMENTS  ON  ACTINIANS 

I.  The  two  preceding  chapters  have  furnished 
proof  of  the  fact  that  the  phenomena  of  purposeful 
reflex  action,  of  spontaneity,  and  of  coordination  are 
determined,  not  by  specific  characters  of  the  ganghon- 
cells,  but  by  general  peculiarities  common  to  all  pro- 
toplasm. These  peculiarities  are  irritability  and  the 
power  of  conducting  stimuli,  both  of  which  will  find 
their  explanation  in  the  physics  of  colloidal  sub- 
stances. 

In  this  chapter  we  wish  to  put  the  foregoing  con- 
clusions to  a  test  by  showing  that  a  group  of  animals 
without  any  true  central  nervous  system  are  able  to 
show  reactions  complex  as  those  in  higher  animals. 
Without  such  a  parallel  we  should  be  more  than 
ready,  in  the  case  of  higher  animals,  to  attribute  such 
reactions  to  the  specific  structure  of  the  ganglia  or 
the  ganglion-cells. 

We  cannot  speak  of  a  central  nervous  system  in 
Actinians  in  the  same  sense  as  in  Ascidians.  Under 
the  ectoderm  there  are  elements  which  are  interpreted 
by  some  authors  as  ganglion-cells  and  nerve-fibres. 

48 


EXPERIMENTS  ON  ACTINIANS  49 

The  unreliability  of  this  interpretation  is  apparent, 
however,  from  the  fact  that  Claus  considers  it  uncer- 
tain. He  mentions  the  possibility  of  a  conduction  of 
stimuli  as  one  of  the  conditions  that  speak  for  the  ex- 
istence of  a  nervous  system  in  Actinians.     But  a  con- 


FiG.  10.     The  Ability  of  the  Actinians  to  Discriminate. 

The  tentacles  press  the  meat  a  into  the  mouth,  while  they  drop  the  water-soaked 
paper  b. 

duction  of  stimuli  also  occurs  in  plants.  During  the 
year  1888  in  Kiel,  and  1889-90  in  Naples,  I  made  in- 
vestigations on  the  reactions  of  Actinians,  which  show 
how  little  reason  we  have  for  concluding  that  compli- 
cated reactions  need  depend  upon  similarly  compli- 
cated reflex  centres  (i).  It  is  very  obvious  from  these 
experiments  that  the  structure  and  irritability  of  the 
peripheral  organs  determine  the  reactions.  We  will 
begin  with  the  description  of  experiments  on  the  Ac- 
tmia  equina  {mesembryanthemurn)  of  the  East  Sea. 


50    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

If  a  wad  of  paper  soaked  In  sea-water  be  placed  on 
the  mouth  of  one  of  these  Actinians  it  Is  refused,  while 
a  piece  of  crab-meat,  which  to  us  does  not  differ  in 
taste  from  the  wad  of  paper,  is  usually  accepted  with- 
out delay.     I  tied  one  end  of  a  short  thread  around  a 


Fig.  II.     Continuation  of  the  Experiment  in  Fig.  id. 

paper  wad  and  the  other  end  around  a  piece  of  meat, 
and  threw  both  on  the  outstretched  tentacles  of  a 
starved  Actinian.  The  tentacles  that  came  in  contact 
with  the  meat  {a,  Fig.  lo)  reacted  at  once  by  bend- 
ing in  such  a  way  as  to  bring  the  meat  to  the  mouth, 
while  the  tentacles  that  were  in  contact  with  the  pa- 
per did  not  react.  I  withdrew  the  thread  and  placed 
it  on  the  oral  disc  in  such  a  way  that  the  paper  rested 
on  the  tentacles  where  the  meat  had  rested  before, 
and  vice  versa.  The  meat  was  then  drawn  into  the 
mouth  and  the  string  with  It,  but  the  paper  remained 
outside  the  oral  opening  (Fig.  1 1).  During  the  next 
twenty-four  hours  no  change  took  place  ;  later  on,  the 
thread  was  ejected  without  the  meat.    The  latter  was 


EXPERIMENTS  ON  ACTINIANS  51 

probably  digested.  I  have  often  repeated  the  experi- 
ment, always  obtaining  the  same  result,  except  that 
occasionally  the  string  was  ejected  sooner,  in  which 
case  the  meat  remained  on  the  string,  partially  or  en- 
tirely undigested.  These  phenomena  have  the  same 
explanation  as  the  behaviour  of  insect-eating  plants. 
The  chemical  substances  diffusing  from  the  meat,  to- 
gether with  the  tactile  stimuli  exerted  by  it,  cause  a 
bending  of  the  tentacles  that  are  touched  in  such  a 
way  that  they  become  concave  and  carry  the  meat  to- 
ward the  oral  opening.  The  contact  of  the  meat 
with  the  mouth  causes  the  sphincter  of  the  oral  open- 
ing to  relax ;  the  pressure  of  the  tentacles,  together 
with  the  activity  of  the  oral  disc,  then  pushes  the  meat 
into  the  interior  of  the  digestive  tract.  But  if  these 
specific  chemical  stimuli  are  wanting,  if  we  give  the 
animal,  for  instance,  water-soaked  filter-paper,  the 
contractions  of  those  muscles  which  carry  the  tenta- 
cles to  the  mouth  are  not  produced.  The  tentacles 
remain  relaxed  or  relax  still  more  under  the  stimulus, 
and  this  fact,  together  with  the  ciliary  movement, 
causes  the  paper  wad  to  fall  off. 

2.  It  is  said  that  the  nerve-elements  are  much  more 
numerous  in  the  vicinity  of  the  mouth  than  in  any  other 
part  of  the  animal.  One  might  think  that  this  con- 
centration of  nerve-elements  determined  the  reflex 
mechanism  for  these  reactions.  For  this  reason,  I 
have  made  use  of  results  obtained  while  carrying 
on  investigations  concerning  heteromorphosis.  I  had 
found   that    in    an   Actinian    of  the    Mediterranean, 


52    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 


Cerianthus  membranaceus,  new  tentacles  could  be  pro- 
duced by  a  lateral  incision  in  the  body  of  the  animal. 
But  in  some  of  these  cases  no  mouth  is  formed.     Fig. 

12  shows  such  an  ani- 
mal ;  a  is  the  normal, 
b  the  new  head.  If  the 
incision  was  very  small, 
only  single  tentacles 
were  formed,  without 
the  oral  disc.  These 
new  tentacles  behave 
toward  food  exactly 
like  the  tentacles  of  the 
old  mouth.  If  we  offer 
such  a  new  head  a 
piece  of  meat,  the  tent- 
acles seize  and  press  it 
against  the  centre  of 
the  oral  disc,  where  the 
mouth  should  be.  After  pressing  in  vain  for  some  min- 
utes the  tentacles  relax  and  the  meat  falls  off.  This 
experiment  could  be  repeated  for  months,  in  fact  as 
long  as  I  observed  the  animal  (2).  In  other  cases  the 
second  head  was  so  near  the  old  one  that  it  was  easy 
to  stimulate  the  tentacles  of  both  simultaneously  with 
the  same  piece  of  meat  In  this  case  a  fight  arose 
between  the  two  tentacle  systems,  each  attempting  to 
draw  the  meat  toward  its  own  oral  disc.  Parker  has 
lately  shown  that  even  a  single  tentacle,  after  being 
severed  from  the  animal,  grasps  a  piece  of  meat  and 


Fig.  12.  AcTiNiAN  (Cerianthus)  with 
A  Normal  Head  {a)  and  an  Arti- 
ficially Produced  Head  {b). 

Although  the  latter  has  no  oral  opening  the  ten- 
tacles carry  the  meat  to  the  place  where  the 
mouth  ought  to  be. 


EXPERIMENTS  ON  ACTINIANS  53 

bends  with  it  toward  the  place  where,  in  relation  to 
itself,  the  mouth  ought  to  be  (3). 

If  we  look  at  these  facts  without  prejudice,  we 
must  conclude  that  the  reaction  of  the  tentacles  is 
determined  only  by  the  irritability  of  the  tentacle- 
elements  themselves,  and  by  the  arrangement  of  their 
contractile  elements.  The  following  observations 
may  also  be  considered  in  support  of  this  conclusion. 

3.  If  an  Actinia  equina  be  divided  transversely,  the 
oral  piece,  which  we  will  call  the  head-piece,  has  the 
normal  head,  with  mouth  and  tentacles  on  its  oral  end  ; 
on  its  aboral  end  the  body-cavity  is  open  to  the 
exterior,  and  food  may  pass  through  the  opening  in 
either  direction.  The  old  mouth  of  a  head-piece  was 
as  particular  as  usual  in  regard  to  the  selection  of  its 
food,  while  the  aboral  end  readily  swallowed  pieces  of 
paper.  The  old  mouth  often  refused  meat,  but  the 
aboral  mouth  was  almost  always  ready  to  accept  it,' 
even  when  it  would  refuse  paper. 
I  I  laid  a  piece  of  an  Actinian  that  took  food  in  at 
both  ends  on  its  side,  and  tried  to  find  out  whether 
both  mouths  would  take  food  simultaneously.  I  first 
placed  a  piece  of  meat  on  the  aboral  mouth,  in  order 
to  cause  it  to  open.  As  soon  as  this  happened  and 
the  meat  was  being  taken  into  the  mouth  I  offered 
the  oral  mouth  also  a  piece,  and  this  was  likewise 
accepted.  The  act  of  swallowing  in  the  other  mouth 
was  interrupted  at  once  by  the  contraction  of  the  ring- 
muscles.  After  a  few  moments,  however,  when  the 
meat    in   the    oral   mouth  had  been   swallowed,   the 


54    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

muscles  of  the  aboral  end  relaxed  and  the  meat  taken 
in  before  by  this  mouth  fell  out.  When  I  fed  the 
mouths  in  succession,  the  mouth  that  was  fed  first 
ejected  the  food  as  soon  as  the  other  began  to  eat. 
It  is  obvious  from  this  that  a  peristaltic  wave  is 
started  from  the  end  which  takes  up  food. 

Thus  far  we  have  considered  only  the  head-piece. 
If  we  turn  our  attention  now  to  the  foot-piece,  we 
find  that  on  the  oral  end  a  new  oral  disc  with  tentacles 
soon  begins  to  form.  Before  this  has  occurred,  how- 
ever, the  mouth  takes  pieces  of  meat  and  swallows 
them.  It  seemed  to  me  as  though  this  new  mouth, 
even  before  the  regeneration  of  the  oral  disc,  re- 
sembled the  normal  mouth  more  than  the  aboral 
mouth  in  the  head-piece,  for  it  did  not  accept  paper 
wads  and  grains  of  sand,  while  It  swallowed  meat 
well. 

4.  In  the  foot  of  the  Actinians  the  contact-irrita- 
bility is  of  special  interest.  The  foot  of  a  normal 
Actinia  equina  attaches  itself  to  the  surface  of  solid 
bodies.  The  character  of  the  surface  is  of  great  im- 
portance for  producing  these  processes  of  attachment. 
If  it  finds  no  other  body,  the  Actinian  attaches  itself 
to  the  glass  of  the  aquarium,  and  glides  about  on  it. 
If,  however,  the  shell  of  a  Mytilus  is  placed  in  the 
aquarium  and  the  animal  comes  in  contact  with  it 
while  moving  about,  it  immediately  attaches  itself  to 
the  shell,  and  remains  there,  whether  the  shell  is 
empty  or  inhabited.  The  surface  of  an  ulva  leaf  has 
the  same  effect.     While  the  animal  upon  contact  with 


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56    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

the  ulva  leaf  will  at  any  time  leave  the  glass  and 
attach  itself  to  the  leaf,  the  reverse  is  not  liable  to 
happen.  This  contact-irritability  of  the  foot  does  not 
change  if  the  head  or  the  greater  oral  part  of  the  ani- 
mal be  amputated.  The  mechanisms  for  the  discharge 
of  these  reactions  must,  therefore,  be  located  in  the 
foot  itself  and  not  in  the  ganglion-cells  of  the  oral  disc. 
5.  In  higher  animals  we  recognise  a  tendency  to  give 
the  body  a  certain  orientation  in  space.  We  usually 
call  such  an  orientation  in  a  higher  animal  its  position 
of  equilibrium.  Certain  Actinians  also  show  such  phe- 
nomena. If  we  put  a  Cerianthus  Into  a  test-tube 
filled  with  sea-water,  and  place  the  glass  so  that  the 
head  of  the  animal  is  down,  the  foot  up,  and  the  long- 
itudinal axis  vertical,  the  tip  of  the  foot  will  begin 
after  a  few  moments  to  bend  downward  vertically. 
In  Fig.  13  the  course  of  such  an  experiment  is  given 
from  life.  Some  minutes  before  12  o'clock  the  ani- 
mal was  placed  in  the  test-tube  in  the  manner  de- 
scribed above.  At  12  o'clock  the  foot  had  begun  to 
bend  downward  (Fig.  13,  ci)\  in  the  next  thirteen 
minutes  the  bending  toward  the  head  had  progressed 
{U)  ;  five  minutes  later  the  foot  had  reached  the  bot- 
tom of  the  tube  {c).  The  bending  progressed  steadily 
to  new  elements  lying  near  the  head  ;  and  since  the 
foot  now  stood  upon  the  bottom  of  the  tube,  the 
farther  advance  of  the  curvature  toward  the  head 
resulted  in  the  lifting  of  the  latter  (Fig.  13,  ^and  ^), 
whereupon  the  animal  raised  itself  bodily,  and  at  i 
o'clock  had  the  position  /.     The  process  of  righting 


EXPERIMENTS  ON  ACTINIANS 


57 


required  one  hour.  The  animal  remained  in  this 
position  for  two  days,  and  then  crawled  out  of  the 
glass. 

In  analysing  the   conditions   that   determine   the 
righting  of  the  Cerianthus  in  this  case,  two  circum- 


FiG.  14.    Cerianthus  Regaining  its  Normal  Orientation. 

It  was  placed  on  the  net  horizontally,  and  within  half  an  hour  had  regained  its  normal 
vertical  position,  by  pushing  itself  through  the  meshes  of  the  net. 

stances  must  be  taken  into  consideration,  namely, 
gravitation  and  the  contact-stimuli.  It  can  be  easily 
shown  that  gravitation  alone  is  able  to  produce  the 
above-mentioned  reaction  of  the  Cerianthus.  A  wire 
net,  whose  meshes  are  so  fine  that  the  body  of  a  Ceri- 
anthus can  only  be  drawn  through  them  by  force, 
is  laid   horizontally    upon   a   glass   standing   in    the 


58    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

aquarium.  A  Cerianthus  Is  laid  on  the  wire  net.  After 
a  few  minutes  the  foot  of  the  animal  begins  to  bend 
downward  and  to  work  its  way  through  one  of  the 
meshes  of  the  net.  In  the  oral  pole  no  change  takes 
place  except  that  the  tentacles  lay  themselves  close  to- 
gether, so  that  they  look  like  a  brush  whose  handle 
is  formed  by  the  body  of  the  animal.  The  animal 
forces  its  body  farther  and  farther  through  the  meshes 
until  it  is  at  last  able  to  keep  itself  in  a  vertical  posi- 
tion as  represented  in  Fig.  14.  This  orientation  can 
be  reached  in  half  an  hour.  If  we  turn  the  wire  net 
over  as  soon  as  the  animal  has  reached  the  position 
represented  in  Fig.  14,  so  that  the  foot  is  up,  it  does 
not  pull  Itself  out  of  the  net  again,  but  the  foot  near 
the  tip  begins  to  bend  downward  vertically.  The 
bending  then  progresses  from  element  to  element  of 
the  body,  from  the  foot  toward  the  head,  until  the  tip 
of  the  foot  reaches  the  wire  net,  when  it  again  pushes 
itself  through  as  far  as  possible.  If  the  wire  net  be 
turned  over  again,  the  process  Is  repeated.  Thus  the 
animal  can  be  forced,  simply  with  the  aid  of  gravit- 
ation, to  weave  itself  in  and  out  of  the  net.  Fig.  15 
shows  a  Cerianthus  that  has  been  forced  to  push  itself 
through  three  times  in  this  manner.  The  drawing 
was  made  from  life.  In  these  experiments  we  have 
an  example  of  a  geotropic  irritability, — in  other  words, 
of  positive  geotropism.  As  this  kind  of  irritability  is 
very  common  in  the  roots  of  plants,  it  follows  that  for 
the  mechanism  of  these  reactions  no  specific  qualities 
of  the  ganglion-cells  are  necessary.      If  a  transverse 


EXPERIMENTS  ON  AC  TIN  I  AN S 


59 


Fig.  15.    AcTiNiAN  that  has  been 
Forced  by  Gravitation  to  Push 

ITSELF  THROUGH    THE  NeT  THREE 

Times  (a,  b,  and  c).     See  text. 


incision  be  made  in  the  middle  of  a  Cerianthus  which 
almost  but  not  quite  separates  the  two  halves,  and  the 
animal  be  placed  immediately  after  the  operation  on 
a  wire  net,  the  foot  works 
itself  into  one  of  the 
meshes  up  as  far  as  the 
incision  and  assumes  a 
vertical  position.  The 
oral  piece,  on  the  con- 
trary, from  the  place  of 
incision  to  the  head,  usu- 
ally remains  lying  hori- 
zontally on  the  net.  This 
shows  that  the  foot  pos- 
sesses geotropic  irritabil- 
ity. But  if  the  Actinian  be  divided  transversely  we 
see  that  the  head-piece  as  well  as  the  tail-piece  pushes 
itself  through  the  meshes,  although  not  so  frequently. 
While  an  Actinian  that  is  suspended  vertically  in  a 
test-tube  or  in  a  mesh  of  a  wire  net  seldom  retains  this 
position  longer  than  two  days,  it  remains  indefinitely 
in  the  sand  after  burrowing.  In  addition  to  gravita- 
tion, some  other  stimulus  must  hold  it  there.  I  be- 
lieve that  it  is  the  contact-stimulus  of  the  sand.  I 
called  this  kind  of  irritability  stereotropism,  and  have 
shown  that  in  a  series  of  animals  it  determines  their 
habits.  Positive  geotropism  and  positive  stereotrop- 
ism cause  the  Cerianthi  to  burrow  in  the  sand  vert- 
ically, and  the  positive  stereotropism  keeps  them 
permanently  in  the  burrow. 


6o    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

We  see  from  this  that  quite  complicated  reactions 
occur  in  these  animals  although  they  do  not  possess  a 
central  nervous  system  like  that  in  higher  animals. 
Were  we  to  come  across  these  same  reactions  in 
higher  animals  we  should  be  inclined  a  priori  to  as- 
cribe them  to  the  complicated  structure  of  the  central 
nervous  system.  The  experiments  on  Actinians  will 
perhaps  prevent  us  from  drawing  such  a  conclusion 
before  we  have  forcible  reasons  for  so  doing.  A  high 
degree  of  complication  in  the  reactions  of  animals  can 
be  reached  where  no  central  nervous  system  exists,  or 
where  it  serves  only  as  a  sensitive  and  quick  proto- 
plasmic conductor.  The  cause  of  complicated  reac- 
tions lies,  therefore,  in  the  irritabilities  and  structures 
of  the  peripheral  organs. 

Bibliography. 

1.  LoEB,  J.  Untersuchungen  zur  physiologischen  Morphologie 
der  Thiere^  I.,  1891.     Wiirzburg,  G.  Hertz. 

2.  LoEB,  J.  Zur  Physiologie  und  Psychologic  der  Aktinien. 
Pflugers  Archiv,  Bd.  lix.,  1895. 

3.  Parker,  G.  H.  The  Reactions  of  Metridium  to  Food  and 
Other  Substances.  Bulletin  of  the  Museum  of  Comparative  Zoology 
at  Harvard  College^  vol.  xxix,,  1896. 

4.  Pollock,  W,  H.  On  Indications  of  the  Sense  of  Smell  in 
ActinicB.     Jour.  Linnean  Soc,  London,  vol.  xvi.,  1882. 

5.  Nagel,  W.  Experimentelle  sinnesphysiologische  Untersuch- 
ungen an  Coelenteraten.     PJlUger's  ArchiVy  Bd.  Ivii.,  1894. 


CHAPTER  V 


EXPERIMENTS  ON  ECHINODERMS 


I.  The  nervous  system  of  the  starfish  consists,  first, 
of  a  central  nerve-ring  around  the  mouth  (Fig.  i6), 
and,  second,  of  the  peripheral  nerves  radiating  from 
this  ring  into  each  of  the  arms. 

It  is  a  well-known 
fact  that  if  such  an  ani- 
mal be  laid  on  its  back 
it  soon  rights  itself.  In 
species  like  that  repre- 
sented in  Fig.  1 6  the 
ambulacral  feet  found 
on  the  ventral  surface 
in  great  numbers  ex- 
ecute the  righting. 
These  little  feet  are 
muscular  tubes,  which 
end  in  a  plate.  By 
means  of  this  plate  the 
foot,  like  the  sucker  of 
the  leech,  can  cling  to  solid  bodies.  If  a  starfish 
be   laid  on  its  back,   the  tube-feet  of  all  the   arms 


Fig.  i6.     Mervous  System  of  a 
Starfish. 

rt,  central  nerve-ring  that  surrounds  the  mouth, 
by  peripheral  nerves  of  the  arms. 


6l 


62    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

are  stretched  out  at  once  and  are  moved  hither  and 
thither  as  if  feeHng  for  something,  and  soon  the 
tips  of  one  or  more  arms  turn  over  and  touch  the  un- 
derlying surface  with  their  ventral  side  (Fig.  17). 
The  tube-feet  of  these  arms  attach  themselves  to  this 


Fig.  17.     Mechanism  of  the  Turning  of  a  Starfish  that  has 
BEEN  Laid  on  its  Back. 

The  tube-feet  of  the  three  arms  at  the  left  are  pulling  while  the  other  two  arms  are  quiet. 
This  causes  the  animal  to  turn  a  somersault  toward  the  left  which  brings  it  again  into 
the  natural  position. 

surface,  and  the  animal  is  then  able  to  turn  a  somer- 
sault and  regain  its  normal  position.  For  this 
result,  it  is  essential  that  all  five  arms  do  not  attempt 
simultaneously  to  bring  the  animal  into  the  ventral 
position.  Should  the  tips  of  all  five,  or  even  four, 
arms  tug  simultaneously,  it  would  be  impossible  for 
the  animal  to  turn  over.  In  normal  starfish  having 
five  arms,  not  more  than  three  begin  the  act  of  turn- 
ing ;   the  other  two  remain  quiet.      If  we,  however, 


EXPERIMENTS  ON  ECHINODERMS  63 

destroy  the  nervous  connection  between  the  arms,  for 
instance,  by  making  two  incisions  at  a  and  b,  Fig.  18, 
this  cooperation  of  the  arms  ceases.  The  normal 
starfish  requires  but  a  few  minutes  to  turn  over,  but 
the  specimen  represented  in  Fig.  18  remained  on  its 


Fig.  18.     The  Same  Experiment  on  a  Starfish  whose  Nerve-Ring 
HAS  been  Severed  in  two  Places  (a  and  b). 

The  right  and  left  arms  are  consequently  no  longer  connected  nervously.  If  such  an  ani- 
mal is  laid  on  its  back,  the  tube-feet  of  four  or  even  all  the  arms  in  most  cases  tug 
simultaneously.     This  prevents  the  animal  from  righting  itself. 

back  the  whole  afternoon,  although  the  arms  were 
struggling  constantly  to  right  it.  The  experiments 
seem  to  indicate  that  in  a  normal  starfish  the  stimulus 
produced  by  the  pulling  of  two  or  three  arms  in  the 
same  direction  has  an  inhibitory  effect  on  the  other 
arms.  This  inhibition  ceases  when  the  nervous  con- 
nection between  the  single  arms  is  broken.     Romanes 


64    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

found  that  a  single  arm  containing  only  the  peripheral 
arm-nerve  rights  itself  when  laid  on  its  back.  Hence 
the  central  nerve-ring  acts  only  as  a  conductor  and 
not  as  a  "  centre  "  for  this  reaction  (i). 

2.  In  analysing  this  righting  reflex  of  the  starfish, 
there  are  two  possibilities  to  be  considered.  Either 
gravity  forces  the  starfish  to  turn  the  ventral  side 
toward  the  centre  of  the  earth,  or  contact-irritability, 
i.  e.,  stereotropism,  forces  the  animal  to  bring  the  vent- 
ral side  in  contact  with  solid  bodies.  The  fact  that 
the  animals  leave  the  horizontal  bottom  of  an  aqua- 
rium and  attach  themselves  to  the  vertical  sides  shows 
that  gravity  is  not  the  cause.  Preyer  made  an  ex- 
periment from  which  he  concluded  that  the  righting 
of  the  starfish  is  due  to  their  being  forced  to  have 
the  ventral  side  down.  He  suspended  a  starfish  in 
the  middle  of  the  aquarium  by  fastening  each  of  its 
arms  by  threads  to  a  cork  that  floated  on  the  surface 
of  the  aquarium.  If  suspended  with  its  back  down, 
Preyer  noticed  that  the  starfish  turned  over.  This 
might  suggest  the  idea  that  the  righting  of  the  star- 
fish is  a  geotropic  phenomenon.  I  have  repeated 
Preyer  s  experiment  and  confirmed  his  observation  (2). 
At  the  same  time,  however,  I  made  a  control  experi- 
ment which  Preyer  omitted.  In  the  beginning  I 
fastened  the  starfish  to  the  cork-plate  in  such  a  way 
that  the  ventral  side  was  turned  toward  the  bottom. 
But  the  starfish  even  then  turned  over.  This  shows 
that  the  suspension  makes  it  restless  and  causes  it  to 
perform  all  sorts  of  turning  movements.     I  believe 


EXPERIMENTS  ON  ECHINODERMS  65 

that  the  ventral  side  of  the  starfish  is  positively  ste- 
reotroplc,  or,  in  other  words,  that  the  starfish  becomes 
restless  if  Its  ambulacral  feet  are  not  in  contact  with 
solid  bodies. 

3.  Preyer  accredits  the  starfish  with  possessing 
*'  intelligence."  He  placed  one  arm  of  an  Ophiuris 
In  a  piece  of  rubber  tubing  in  order  to  see  whether 
the  animal  would  be  clever  enough  to  rid  itself  of  this 
impediment  to  its  movements.  He  found  that  after 
a  time  the  arm  "  freed  itself  "  from  the  tube.  I  have 
repeated  the  experiment  in  these  animals  and  found 
that  the  Ophiuris  pays  no  attention  to  the  rubber 
tube.  The  animal  of  course  loses  it  after  a  time  un- 
less it  fits  too  closely,  but  it  Is  always  purely  a  matter 
of  chance,  and  there  is  no  more  intelligence  involved 
than  the  clothes-line  displays  when  the  clothes  are 
blown  from  it  by  the  wind.  Romanes  found  that 
when  one  arm  of  a  starfish  is  stimulated  the  animal 
moves  in  a  direction  opposite  to  the  stimulated  arm. 
This  also  looks  like  intelligence,  for  the  animal  seems 
to  be  able  to  avoid  a  danger.  The  late  Professor 
Norman  called  my  attention  to  the  fact  that  when 
one  arm  of  a  starfish  Is  stimulated  the  feet  of  this 
arm  are  drawn  in  and  the  arm  becomes  inactive. 
This  is,  however,  only  true  of  the  stimulated  arm  ; 
the  others  remain  active.  Therefore,  according  to  the 
parallelogram  of  forces,  a  movement  away  from  the 
point  of  stimulation  will  take  place.  Intelligence 
plays  no  part  in  this  phenomenon. 

4.  The   tendency    to   crawl    upwards   on    vertical 


66    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

surfaces  is  a  pronounced  reaction  of  Echinoderms  and 
is  quite  common  in  other  animals,  for  instance  in  the 
Actinia  fnesembryanthemum  of  the  Mediterranean, 
and  in  the  CoccinelH.  This  tendency  is  also  present 
in  plant-organisms  —  for  example,  Plasmodia, —  and 
here  Sachs  has  traced  it  back  to  negative  geotrop- 
ism.  I  will  repeat  here  the  description  which  I  have 
already  given  in  a  former  publication  of  the  phenome- 
non as  it  appears  among  Echinoderms  (3). 

No  one  who  observes  the  animals  on  rocks  or  posts 
near  the  surface  of  the  ocean  when  the  water  is  quiet 
can  fail  to  notice  the  relatively  large  number  of 
Echinoderms.  Many  of  these — for  example,  the  Cu- 
cumaria  cucumiSy  which  is  very  common  in  the  Bay 
of  Naples — always  live  near  the  surface,  not  beyond  a 
depth  of  about  30  m.  It  can  be  shown  that  Cucuma- 
ria,  like  Plasmodia  or  CoccinelH,  are  forced,  when  on 
vertical  surfaces,  to  crawl  upward.  Cucumaria  has  a 
slender  pentagonal  body,  10  cm.  or  more  in  length, 
with  radial,  branching  tentacles  on  its  oral  end. 
There  are  five  ridges  on  the  body,  and  in  these  are 
situated  longitudinal  rows  of  tube-feet,  by  means  of 
which  the  animal  crawls  upward,  even  on  smooth 
glass  walls.  If  placed  in  an  aquarium,  it  crawls  about 
on  the  bottom  until  it  comes  to  a  vertical  side  ;  it  then 
crawls  upward  and  remains  on  the  highest  point,  if 
possible  just  below  the  surface  of  the  water.  This 
position  then  usually  becomes  permanent,  and  the 
animal  is  converted  into  a  sessile  organism. 

If   a   Cucumaria   is    allowed  to    attach  itself  to  a 


EXPERIMENTS  ON  ECHINODERMS 


67 


vertical  glass  which  can  be  revolved  around  a  hori- 
zontal axis  in  the  aquarium,  it  will  crawl  upward 
whenever  the  glass  is  turned.  This  is  not  a  compen- 
satory movement  produced  by  the  centrifugal  force, 
for  during  the  rotation  of  the  glass  the  animal  re- 


vyyyyyyyyyyyyyyyyyyyy/'yyyyyyyyyyy/:>Z7zy.^ 


Fig.  19.     Geotropic  Reaction  of  Cucumaria  Cucumis. 

The  animals  are  in  a  battery  jar  (a,  ^,  f ,  <f ).  It  is  filled  with  water  and  rests  on  the  bridge 
B  B  in  the  aquarium  A  A.  Running  water  is  supplied  through  the  tube  ^  at  o.  They 
collect  at  the  highest  point  (^,  d)  of  the  glass. 

mains  quiet,  and  not  until  a  quarter  or  half  an  hour 
after  the  rotation  does  it  begin  to  migrate  upward. 
Neither  is  the  upward  migration  caused  by  the  light 
falling  in  from  above.  If  the  animals  are  placed  in 
an  aquarium  in  which  light  is  allowed  to  enter  only 
from  the  side  or  from  below,  they  will  still  crawl  up- 
ward on  the  vertical  sides.  In  a  dark  room  they  be- 
have just  as  they  do  in  the  light. 

One  might  believe  that  the  need  of  oxygen  determ- 
ined the  upward  migration  of  the  Cucumarise  to  the 


L 


68    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

surface  of  the  water.  It  can  be  shown,  however,  that 
this  is  not  the  case.  If  a  large  beaker  filled  with 
water  be  placed  inverted  in  the  aquarium,  the  Cucu- 
mariae  that  are  under  the  beaker  begin  to  creep  up  to 
the  bottom  of  the  glass.  They  also  do  so  when  the 
experiment  is  made  in  the  manner  represented  in  Fig. 
19.  A  bridge  B  B  is  placed  in  the  aquarium  A  A, 
the  horizontal  part  of  the  bridge  B  B  being  below 
the  surface  of  the  water  of  the  aquarium.  The  hori- 
zontal part  has  a  round  opening  o  over  which  the  in- 
verted beaker  abed  filled  with  water  Is  placed.  Fresh 
water  is  supplied  at  a  low  pressure  at  0  through  a 
glass  tube^,  which  has  been  properly  bent.  The  Cu- 
cumarise  nevertheless  go  away  from  0  and  remain  at 
the  highest  point  c  d,  or  near  cd  on  the  vertical  sides 
(Fig.  19),  where  they  ultimately  die. 

Experiments  on  the  centrifugal  machine  yielded  no 
result,  for  the  animals  did  not  move  during  the  rota- 
tion. Gravity  is  the  only  condition  which  can  account 
for  the  phenomenon,  and  I  imagine  the  influence 
which  gravity  exercises  to  be  in  a  manner  similar  to 
that  observed  among  insects — for  example,  in  butter- 
flies which  have  just  emerged  from  the  chrysalis. 
The  wings  of  the  butterfly  do  not  unfold  immediately, 
and  it  runs  about  restlessly  until  it  comes  to  a  vertical 
surface.  When  this  is  reached,  the  butterfly  creeps 
upon  it  and  remains  there  for  some  time  with  its  head 
up.  After  the  wings  are  spread,  other  conditions 
cause  the  animal  to  be  restless  again. 

Because  of  this  dependence  on  gravity,   the    Cu- 


EXPERIMENTS  ON  ECHINODERMS  69 

cumarlae  are  of  necessity  inhabitants  of  the  surface- 
regions  of  the  ocean.  If  a  larva  were  carried  down 
to  a  great  depth,  its  negative  geotropism  would  force 
it  to  migrate  upward  until  the  highest  point  was 
reached  or  until  death  put  an  end  to  its  upward 
journey. 

Certain  starfish  —  for  instance  Asterina  gibbosUy 
which  also  lives  near  the  surface  of  the  water — behave 
like  Cucumaria.  All  the  experiments  I  have  made 
on  Cucumaria  can  likewise  be  successfully  performed 
on  Asterina  gibbosa,  but  with  the  difference  that  the 
exceptionally  voracious  Asterina  does  not  remain  per- 
manently at  the  highest  point  of  the  vertical  surface. 
In  two  days,  or  sometimes  even  sooner,  it  begins  to 
move  or  drops  down. 

Positive  heliotropism  naturally  has  the  same  effect 
as  negative  geotropism.  Asterina  tenuispina,  like  As- 
terina gibbosa,  lives  at  the  surface  of  the  sea.  It  is 
not,  however,  geotropically  irritable  ;  but  it  is  posi- 
tively heliotropic.  I  put  a  large  number  of  specimens 
of  both  species  in  a  heap  in  an  aquarium,  into  which 
rays  of  light  from  one  side  only  fell  nearly  horizon- 
tally. In  a  short  time  the  two  species  had  parted, 
the  Tenuispinse  crawling  off  on  the  floor  toward  the 
source  of  light.  The  Gibbosse,  scattered  about  on 
the  bottom  of  the  aquarium  in  every  direction, 
crawled  up  the  vertical  sides  without  being  influ- 
enced at  all  by  the  light  in  their  movements.  In  the 
ocean,  where  the  vertical  rays  of  daylight  are  chiefly 
concerned    in    the    orientation    of    animals,    positive 


*]o    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

heliotropism  must  drive  Asterina  tenuispina  to  the 
surface  of  the  ocean,  just  as  Asterina  gibbosa  is  driven 
there  by  negative  geotropism. 

Preyer  mentions  briefly  in  his  extensive  work  on 
The  Movements  of  the  Starfish  the  ''  tendency  of  these 
animals  to  move  upwards."  "  The  strong  tendency  of 
starfish  and  brittlestars  to  go  upward  cannot  be  traced 
back  to  lack  of  air,  lack  of  food,  changes  in  tempera- 
ture or  current,  or  to  a  desire  for  light,  for -they  climb 
up  just  the  same  when  these  conditions  are  eliminated. 
Probably  some  peculiarity  of  the  bottom,  or  of  just 
that  part  of  the  bottom  where  the  animal  is,  makes  it 
unsuitable  for  the  suction  of  the  tube-feet.  The  ani- 
mals can  remain  there  no  longer,  so  they  move  up- 
wards. But  it  is  possible  that  parasites,  which  I  have 
often  found  in  the  ambulacral  furrows,  may  cause  this 
upward  migration,  for  as  the  stimuli  produced  by 
them  come  from  below,  they  might  seem  to  belong  to 
the  bottom." 

The  first  sentence  in  this  generalisation  is  wrong ; 
the  light  attracts  Asterina  tenuispina  upwards.  Sec- 
ond, the  character  of  the  bottom  does  not  determine 
the  phenomenon.  If  Asterina  gibbosa  be  placed  in  a 
cubical  box  with  glass  sides,  the  animals  leave  the 
basal  horizontal  side  and  crawl  up  the  vertical  sides. 
If  the  box  then  be  turned  90°  around  a  horizontal 
axis,  the  side  which  is  now  basal  is  deserted  by  the 
animals.  They  crawl  up  and  remain  on  the  side 
which,  while  horizontal,  they  had  left.  Finally,  if 
Preyer  believed  that  parasites  force  the  animals  to 


EXPERIMENTS  ON  ECHINODERMS  71 

crawl  upward,  it  is  difficult  to  see  why  they  should 
not  drive  the  animals  down  from  the  vertical  side. 
As  a  fact,  however,  Asterina  gibbosa^  as  well  as  Cucu- 
maria  ctccufnis,  remains  on  the  highest  point  of  the 
vertical  side.  I  believe  it  is  much  nearer  the  truth  to 
ascribe  the  vertical  upward  movements  of  certain 
starfish  to  an  action  of  the  force  of  gravity. 

Bibliography. 

1.  Romanes,  G.  J.    Jelly-fish^  Starfish  and  Sea  Urchins.     New 
York,  1893. 

2.  Preyer,    W.       Ueber   die   Bewegung  der   Seesterne.      Mit- 
theilungen  aus  der  zoologischen  Station  zu  Neapel^  Bd.  vii,  S.  96. 

3.  LoEB,  J,      Ueber  Geotropismus  bet  Thieren.     Pfliiger's  Ar» 
chiv^  Bd.  xlix,  1891. 


CHAPTER  VI 


EXPERIMENTS  ON  WORMS 


I.  We  shall  consider  separately  in  this  chapter  two 
kinds  of  worms  :  first,  those  in  which  the  ganglia  are 

all  crowded  together  in 

rN^ ^      the     head    end  —  e.    g., 

Planarians  ;  and  second, 
those  with  a  series  of 
segmental  ganglia  —  e. 
g.,  Annelids. 

Sea-  and  fresh  -  water 
Planarians  differ  little 
structurally,  yet  they 
may  show  different  re- 
actions upon  losing  the 
oral  ganglion. 

Thysanozoon  (Broc- 
chii).  Fig.  20,  a  marine 
Planarian,  is  very  com- 
mon in  the  Bay  of  Na- 
ples. It  is  from  i  to  3 
cm.  long  and  nearly  as  broad.  The  oral  end  of 
the  body,  which  can  be  recognised  by  two  tentacles 


Fig 


ThysanozoOn  Brocchii, 
Marine  Planarian. 


^,  brain  ;  w,  mouth ;  «,  longitudinal  nerve. 
(Diagrammatic  after  Lang.) 


72 


EXPERIMENTS  ON  WORMS 


73 


(^,  Fig.  20),  contains  the  brain  of  the  animal.  This 
consists  of  two  connected  gangHa,  from  which  a  series 
of  nerves,  containing  single  ganglion-cells,  go  out ; 
among  the  latter,  the 
two  large  longitudinal 
nerves  running  length- 
wise throughout  the 
animal  {n,  Fig.  20)  are 
conspicuous.  In  the 
periphery  a  plexus  is 
formed  (i).  The  central 
nervous  system  consists 
of  the  double  ganglion 
in  the  forward  end. 
Like  all  Planarians, 
Thysanozoon  crawls  on 
the  side  of  the  aquarium 
or  on  the  surface  film 
of  the  water.  It  differs 
from  the  fresh  -  water 
Planarians  in  being  able 
to  perform,  in  addition,  genuine  swimming  move- 
ments. With  the  sides  of  its  body  it  makes  vibra- 
tions similar  to  those  made  by  the  wings  of  a  but- 
terfly. If  while  a  Thysanozoon  is  gliding  about  on 
the  surface  of  the  water  it  be  divided  transversely 
with  a  pair  of  scissors,  the  posterior  or  aboral  half 
{b,  Fig.  21)  at  once  falls  to  the  bottom,  while  the 
oral  piece  {a.  Fig.  21)  containing  the  brain  creeps 
on    undisturbed.     If  the   division    be    made    with   a 


Fig.  21. 


Thysanozoon  Divided 
Transversely. 


The  anterior  piece  a,  containing  the  brain,  shows 
spontaneity  ;  the  posterior  piece  b,  none. 


74     COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

sharp  knife  while  the  Planarian  is  crawling  on  a 
glass  plate,  the  oral  piece  (a,  Fig.  21)  crawls  on  un- 
disturbed, while  the  progressive  movement  of  the 
posterior  piece  ceases  entirely.  The  spontaneity  of 
the  progressive  movement  of  the  Thysanozoon  is 
then  a  function  of  the  part  of  the  body  containing 
the  brain  (2). 

In  a  Thysanozoon  that  has  been  divided,  both  pieces 
live  and  regenerate  the  lacking  parts.  The  oral  piece, 
however,  regenerates  more  rapidly  than  the  aboral 
piece,  which  has  to  form  a  head.  I  have  not  investi- 
gated whether  the  latter  also  forms  a  new  brain.  I 
kept  such  pieces  alive  for  four  months.  The  spon- 
taneity of  the  posterior  piece  never  returned ;  the 
spontaneity  of  the  anterior  piece  remained. 

If  we  put  a  normal  Thysanozoon  on  its  back  it  soon 
rights  itself.  The  question  now  arises  whether,  like 
the  progressive  movements,  these  righting  movements 
are  a  function  of  the  brain.  This  is  not  the  case.  A 
Thysanozoon  from  which  the  brain  has  been  removed 
rights  itself  if  laid  on  its  back,  only  the  reaction  pro- 
ceeds more  slowly  than  in  the  normal  animal,  or  even 
in  a  piece  of  an  animal  if  this  piece  contains  the  brain. 
We  see  here  again  that  the  nervous  system  only 
serves  to  bring  about  a  quicker  reaction. 

If,  instead  of  dividing  the  Thysanozoon  completely, 
we  leave  the  two  parts  on  one  side  connected  by  a 
thin  piece  of  tissue  in  such  a  way  that  (Fig.  22)  the 
posterior  piece  can  receive  no  direct  innervations 
from    the    brain    through    the    longitudinal    nerves. 


EXPERIMENTS  ON  WORMS 


75 


conduction  of  stimuli  would  still  be  possible  through 
the  side  nerve-plexus. 

Such  an  animal  was  placed  after  the  operation  on 
the  bottom  of  the  aquari- 
um ;  the  anterior  piece  im- 
mediately began  to  move, 
while  the  posterior  piece 
attempted  to  attach  itself 
to  the  bottom.  The  latter 
soon  yielded  to  the  tugging 
of  the  oral  piece,  however, 
and  took  part  in  its  pro- 
gressive movements  in  an 
entirely  coordinated  man- 
ner, as  though  no  incision 
had  been  made.  After  a 
time  the  oral  piece  turned 
around  and  crawled  over 
the  back  of  the  posterior 
piece,  which  was  dragged  behind  passively,  and  was 
turned  on  its  back.  It  righted  itself  immediately  and 
moved  off  actively  in  the  same  direction  as  the  oral 
piece.  Changes  of  direction  originated  only  in  the 
piece  containing  the  brain  and  were  never  transmitted 
directly  to  the  posterior  piece.  But  if  the  oral  piece 
continued  for  a  time  to  move  in  the  same  direction 
and  with  the  same  rapidity,  the  same  movement  would 
soon  take  place  in  the  posterior  piece.  Hence  the 
posterior  piece  did  not  behave  entirely  like  a  piece 
from  which  the  brain  had  been  removed,  for  it  made 


Fig.  22.     ThysanozoOn  with 
Transverse  Incision. 


76     COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

progressive  movements,  nor  yet  like  a  normal  Thy- 
sanozoon  for  it  had  lost  its  spontaneity.  This  becomes 
still  more  apparent  from  the  following  observation  : 
I  threw  a  Thysanozoon  similarly  operated  upon  into  a 
tank  of  water.  Both  pieces  performed  synchronic 
swimming  movements.  The  oral  piece  soon  reached 
the  vertical  side  of  the  aquarium  and  began  to  creep 
upwards.  As  a  result  of  the  change  of  direction  in 
the  anterior  piece,  the  tissue  connecting  the  two  parts 
became  twisted  and  the  back  of  the  posterior  piece 
came  in  contact  with  the  glass,  while  the  ventral  side 
was  turned  toward  the  water.  It  then  made  swim- 
ming movements  and  in  this  way  followed  the  crawl 
ing  movements  of  the  oral  piece.  The  posterior 
piece  therefore  is  not  simply  dragged  behind  passively, 
but  takes  an  active  part  in  the  progressive  movement 
when  the  movements  are  continuous.  This  is  also 
evident  from  the  fact  that  it  would  often  crawl  along 
on  the  back  of  the  oral  piece,  especially  if  the  latter 
suddenly  began  to  move  more  slowly. 

These  experiments  show  that  a  Thysanozoon  from 
which  the  brain  has  been  removed  no  longer  moves 
spontaneously,  nor  is  it  possible  to  produce  progress- 
ive movements  in  it  by  any  external  stimulus.  If 
touched,  local  contractions,  only,  result. 

2.  The  brain  and  nervous  system  of  the  fresh-water 
Planarians  (Fig.  23,  from  Jijima)  are  so  similar  to  those 
of  the  marine  Planarians  that  for  our  purpose  it  is  un- 
necessary to  give  a  special  description  of  them.  The 
principal  difference  is  probably  that  the  two  longitu- 


EXPERIMENTS  ON  WORMS 


77 


G 


dinal  nerves  contain  a  greater  number  of  ganglion- 
cells,  so  that  they  almost  form  segmental  aggregations. 
From  this  similarity  we  should  Infer  that  the  brain- 
functions  of  the  fresh-water  Plana- 
rlans  would  be  analogous  to  those 
of  the  Polyclads.  However,  such 
is  not  the  case.  If  we  divide  a 
fresh-water  Planarian,  for  instance 
Planarta  torva,  transversely,  the 
posterior  half,  that  has  no  brain, 
crawls  just  as  well  as  the  oral  half. 
Spontaneity  In  Planarta  torva  is, 
therefore,  by  no  means  a  function 
of  the  brain.  Every  piece  of  the 
animal  that  Is  not  too  small  pos- 
sesses spontaneity.  The  decap- 
itated animals  crawl  with  the 
anterior  end  in  front  like  normal 
animals  (2). 

The  question  now  arises  as  to 
how  it  happens  that  in  Thysano- 
zoon  spontaneous  movements  cease 
if  the  head  be  amputated,  while  in 
fresh-water  Planarians  this  opera- 
tion does  not  have  such  a  result, 
to  account  for  the  difference  by  the  fact  that  the 
fresh-water  Planarians  have  more  ganglion-cells 
throughout  the  longitudinal  nerves  than  the  Thysano- 
zoon.  With  the  aid  of  comparative  physiology  it  is 
possible  to  show  that  such  a  view  Is  untenable.     In 


Fig.  23.  Fresh- Water 
Planarian  (Plana- 
RiA  Torva). 

G^  brain,  m,  longitudinal  nerve. 
(After  Jijima.) 

One  is  tempted 


L 


78    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

the  crayfish,  the  suboesophageal  ganglion  with  the 
ventral  ganglion  chain  represents  a  much  more  highly 
developed  ganglion-system  than  the  longitudinal 
nerves  in  Planaria  torva.  We  shall  see,  nevertheless, 
that  a  crayfish,  which  possesses  these  ganglia,  but 
has  lost  the  supracesophageal  ganglion,  no  longer 
moves  spontaneously.  We  shall  see,  furthermore, 
that  a  frog  that  has  lost  the  cerebral  hemispheres  and 
thalamus  opticus  does  not  move  spontaneously,  al- 
though it  possesses  many  more  ganglia  in  the  spinal 
cord  than  Planaria  torva.  The  same  frog,  however, 
moves  spontaneously  again  if,  in  addition,  the  optic 
lobes  and  the  pars  commissuralis  of  the  medulla 
oblongata  be  removed. 

Spontaneous  progressive  movements  are  not  a 
specific  function  of  ganglia  or  of  ganglion-cells  ;  we 
observe  them  even  in  the  swarmspores  of  algse  and 
in  bacteria.  Why  the  decapitated  Thysanozoon  no 
longer  performs  progressive  movements,  and  a  decap- 
itated fresh-water  Planarian  continues  to  move  spon- 
taneously, we  are  not  yet  prepared  to  say.  It  is 
possible  that  the  difference  between  fresh-water  and 
marine  Planarians  is  somewhat  of  the  same  character 
as  that  between  Hydromedusse  and  Acalephse.  In 
the  latter,  both  parts,  margin  and  centre,  beat  rhyth- 
mically in  sea-water,  while  in  the  Hydromedusse  only 
the  margin  with  the  nerve-ring  is  able  to  do  so.  But 
we  were  able  to  show  that  this  difference  between  the 
two  classes  of  Medusae  is  not  so  much  due  to  mor- 
phological   differences    as  to    chemical    or   physical 


EXPERIMENTS  ON  WORMS  79 

differences.  A  reduction  in  the  amount  of  Ca  ions 
in  the  sea-water  allowed  the  centre  of  a  Hydromedusa 
to  beat  spontaneously.  The  case  of  marine  Planarians 
may  be  similar,  and  further  experiments  may  yield  the 
result  that  with  a  change  in  the  constitution  of  the 
sea-water  the  posterior  half  of  a  Thysanozoon  will 
be  able  to  show  spontaneous  locomotion. 

The  behaviour  of  Planaria  torva  toward  light  is  of 
special  interest.  The  animal  is  especially  sensitive  to 
changes  in  the  intensity  of  light.  If  brought  from 
the  dark  into  the  light  suddenly,  it  begins  to  move. 
At  first  the  direction  of  the  movements  seems  to  be 
influenced  by  the  light,  for  the  animals  move  away 
from  the  source  of  light  as  if  they  were  negatively 
heliotropic.  However,  they  do  not  collect  at  the  point 
farthest  from  the  source,  as  do  negatively  heliotropic 
animals,  but  they  scatter  in  all  directions  and  come  to 
rest  at  last  in  a  place  where  the  light  is  comparatively 
weakest.  From  this  it  would  seem  that  an  increase 
in  the  intensity  of  light  causes  them  to  move,  while 
a  decrease  in  the  intensity  of  light  causes  them  to 
rest.  This  would  account  for  the  fact  that  we  find 
them  by  day  always  under  stones  or  in  relatively  dark 
places.  I  suspect  that  they  begin  to  move  about  in 
the  night,  and  that  they  come  to  rest  when  day 
returns.  I  have  repeatedly  tried  the  experiment  of 
covering  in  the  morning  one-half  of  the  dish  with 
black  paper.  During  the  day  no  change  takes  place, 
but  the  next  morning  all  the  animals  are  found  under 
the  covered  portion  of  the  dish.     The  only  possible 


8o    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

explanation  for  this  behaviour  is  that  they  crawl  about 
in  the  dish  during  the  night  and  in  the  morning  stop 
in  the  darkest  place.  These  animals  have  at  their 
oral  pole  not  only  a  brain  but  also  comparatively  well- 
developed  eyes.  I  resolved  to  try  whether  a  decapit- 
ated Planarian,  in  spite  of  the  loss  of  brain  and  eyes, 
would  still  show  the  same  reactions  toward  light  as 
the  normal  animals.  This  is  the  case  to  a  most  sur- 
prising extent.  In  the  evening,  about  sixty  specimens 
of  Planaria  torva  were  cut  transversely  just  behind 
the  brain  and  eyes.  All  the  pieces  were  put  into  a 
dish  with  vertical  sides  which  was  half  covered  with 
black  paper.  The  next  morning  nearly  all  the  pieces, 
posterior  as  well  as  anterior,  were  found  in  the  covered 
portion  of  the  aquarium,  where  they  were  scattered 
about  pretty  uniformly.  In  the  uncovered  portion  of 
the  dish  I  found  a  few  pieces,  anterior,  however,  as 
well  as  posterior  ones,  crowded  together  in  a  corner 
where  the  intensity  of  the  light  was  a  comparative 
minimum.  Upon  repeating  this  experiment  with  nor- 
mal Planarians,  the  same  result  was  obtained.  When 
the  decapitated  animals  were  at  rest  in  the  covered 
portion  of  the  dish,  their  rest  was  soon  disturbed  if, 
without  jarring  the  aquarium,  the  dark  paper  was 
removed  suddenly.  At  first  they  crawled  about  on 
the  side  away  from  the  light,  then  they  collected 
again  where  the  intensity  of  light  was  a  relative  mini- 
mum. This  reaction  occurred  just  as  in  normal  ani- 
mals, except  that  the  reaction-time  of  the  brainless 
animals  was  greater  than  in  normal  animals.      In  the 


EXPERIMENTS  ON  WORMS 


8i 


pieces  containing  brain  and  eyes,  the  reaction  be- 
gan about  one  minute  after  exposure  to  light ;  in  the 
pieces  without  brain,  after  about  ^m^  minutes.  In  this 
experiment,  only  diffused  daylight  was  employed  as  a 
stimulus.  In  a  round  dish  with  vertical  sides,  the 
Planarians  do  not  collect,  like  strictly  heliotropic  ani- 
mals, on  the  window-  or  room-side  of  the  dish,  but  on 
the  right  and  left  sides.  Decapitated  Planarians  be- 
have in  the  same  way.  All  these  reactions  occur  the 
day  after  the  operation.  Fresh 
material  should  always  be  used  for 
these  experiments. 

After  what  has  been  said,  it  is 
hardly  necessary  to  mention  that 
pieces  of  Planar ia  torva  from  which 
the  brain  has  been  removed  right 
themselves  as  well  as  normal  animals. 

According  to  some  authors,  the 
starfish  represents  a  colony  of  as 
many  individuals  as  it  has  arms. 
We  have  seen  that  these  react  har- 
moniously as  long  as  the  nervous  fig.  24.  two-headed 
connection  is  uninterrupted.  In 
Actinians  that  have  been  made  two- 
headed  artificially,  this  harmony  no 
longer  exists  ;  for  instance,  in  taking  food  both  heads 
struggle  for  the  same  piece  of  meat.  At  my  suggest- 
ion. Dr.  van  Duyne  tried  to  produce  multi-headed 
Planarians  artificially.  He  succeeded  in  making 
them  with  as  many  as  six  heads.     Fig.  24  shows  a 


Planarian  Produced 
Artificially.  (After 
van  Duyne.) 


\ 


82    COMPARA  TIVE  PHYSIOLOG  V  OF  THE  BRAIN 

two-headed  specimen.  If  the  heads  were  far  enough 
apart,  they  no  longer  moved  synchronically    in  the 

same  direction, 
in  which  case 
the  pulHng  in 
opposite  direc- 
tions (Fig.  25) 
was  so  stronof 
that  the  animal 
was  torn  asun- 

FiG.  25.     Planarian  with  two  heads  that  are  ,        ,   . 

Attempting  to  Move  in  Opposite  Directions,  ^^^  v   /* 

AND  IN  so  Doing  are  Tearing  the  Common  %,    In  the  An- 

BODY.     (After  van  Duyne.)  ^^^jj^^    ^^     ^^^ 

a  segmental  arrangement  of  the  central  nervous  sys- 
tem. This  type  of  structure  is  also  found  in  Arthro- 
pods and  in  Vertebrates.  It  will  perhaps  make  our 
task  easier  if  we  conceive  the  segmented  animal  to  be 
a  colony  of  as  many  individuals  or  animals  as  there 
are  segments  (or  ganglia)  present  in  the  body.  Each 
segment  is  then  comparable  to  an  Ascidian  in  which 
the  central  nervous  system  consists  of  but  one  gan- 
glion. The  fibres  and  cells  of  each  ganglion  form 
for  the  corresponding  segment  a  protoplasmic  bridge 
between  the  skin  and  muscles.  A  stimulation  be- 
ginning, however,  in  one  segment  is  not  confined  to 
that  segment,  for  the  single  ganglia  of  the  various 
segments  are  connected  with  each  other  by  means  of 
nerve-fibres,  the  so  called  longitudinal  commissures. 
By  means  of  these,  a  stimulation  which  originates  in 
one  segment  is  transmitted  also  to  the  neighbouring 


EXPERIMENTS  ON  WORMS 


83 


/  _^— .u. 


ganglia  and  from  these  to  those  farther  away,  until  at 
last  it  reaches  the  end  of  the  animal. 

The  central  nervous  sys- 
tem of  Annelids  corre- 
sponds to  the  spinal  cord 
of  Vertebrates  and  consists 
simply  of  a  chain  of  ganglia. 
These  lie  entirely  on  the 
ventral  side  of  the  animal, 
with  the  exception  of  the 
most  anterior  (supraoeso- 
phageal)  ganglion  (Fig. 
26),  which  lies  above  the 
oesophagus  on  the  dorsal 
side.  This  is  connected 
with  the  suboesophageal 
ganglion  by  a  double  com- 
missure, which  forms  a  loop 
through  which  the  oesopha- 
gus passes.  It  may  be 
called  the  brain,  although 
the  small  analogy  exist- 
ing between  Vertebrates 
and  worms  makes  the  use 
of  the  term  purely  arbi- 
trary. 

A    question    of    funda- 
mental interest  to  us  arises 
at  this  point  :  Is  the  brain  simply  a  segmental  gan- 
glion, or  is    it   an    organ   of   a   higher   order  which 


Fig.  26.  The  Brain  and  a  Series 
OF  Segmental  Ganglia  of  an 
Annelid  (Nereis). 

Oy  supraoesophageal  ganglion  or  brain  ;  c, 
commissure  ;  «,  suboesophageal  ganglion. 
(After  Claparede.) 


S4    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 


a. 


Ge- 


regulates    and    guides    the    activity    of    the    other 
gangha  ? 

In  our  analysis  of  the  nerve-functions  we  will  begin 
with  the  earthworm.  We  will  consider  first  its  pro- 
gressive movements,  and  will  attempt  to  answer  the 
question,  Does  coordinated  progressive  movement,  in 

which  all  the  segments  of 
the  body  participate,  de- 
pend upon  the  brain  (^, 
Figs.  27  and  28)  ?  The 
locomotion  of  the  earth- 
worm is  a  very  simple 
process.  The  setae  play 
an  important  role,  although 
they  are  not  visible  to  the 
naked  eye ;  they  act  like 
locomotor  appendages  and 
give  the  animal  a  hold  on 
Fig.  27.  Dorsal  View  of  the  Cen-  the  ground.  The  real  mus- 
TRAL  Nervous  System  of  an  ^|^g  ^£  locomotion,  how- 
Earthworm.  .  ' . 

ever,  are  contamed  m  the 

Oy  supraoesophageal  ganglion  ;  c,  commissure ; 

«,  suboesophageal  gangUon  ;  6-,  pharynx ;     CUtaUeOUS         mUSCle   -   layer. 
G,  ganglia  of  the  ventral  cord.  ,    .  .  -       .  _ . 

This  consists  01  ring-nbres 
and  longitudinal  fibres.  When  the  worm  begins  to 
move,  the  ring-fibres  contract  first,  causing  the  worm 
to  become  longer  and  thinner.  The  bristles  are 
turned  backward  and,  because  of  the  resistance  of 
the  ground,  prevent  the  animal  from  moving  back- 
ward. In  this  way  the  head  is  pushed  forward.  As 
soon  as  the  maximum  elongation  has  been  reached, 


EXPERIMENTS  ON  WORMS 


85 


the  longitudinal  muscles  contract  and  the  worm 
becomes  shorter.  As  the  bristles  are  still  turned 
backward,  the  shortening  can  only  be  accomplished 
by  the  approach  of  the  posterior  end  toward  the 
head.  The  entire  worm  is  therefore  compelled  to 
move  forward.     What  happens  if  ^ 

we  divide  the   ganglion-chain  of  / 

the  animal  in  the  middle  of  the 
body,  or  if  we  remove  some 
ganglia  from  that  region  ?  Will 
the  forward  piece  move  inde- 
pendently of  the  posterior  piece  ? 
Benedict  Friedlander  has  made 
this  experiment  and  found  that 
the  coordination  continues  in  spite 
of  the  division  of  the  central  ^^Z~ 
nervous  system  (4).  If  the  for- 
ward piece  begins  to  move,  the 
aboral  piece  will  also  move  in  the 
same  direction  and  at  the  same 
rate.  This  overthrows  the  idea 
that  coordination  in  these  animals 
is  determined  by  a  special  centre  '^  '"fpraoesophageai  ganguon  or 

J  ^  brain  ;      «,     subcesophageal 

of  coordination  which  is  located  in       ganglion;  a  intestine;  c, 

.  T-»  1  1  1  ganglia  of  the  ventral  cord. 

the  bram.  But  how,  then,  does 
the  coordination  take  place  ?  When  the  forward 
piece  elongates  and  attempts  to  shorten  itself  by 
contracting  the  longitudinal  muscles,  the  skin  of  the 
aboral  piece  is  stretched.  This  pulling  probably 
acts   as    a   stimulus    which    causes   the    longitudinal 


Fig.  28.  Side  View  OF  THE 
Central  Nervous  Sys- 
tem OF  THE  Earth- 
worm. 


\ 


86     COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

muscles  of  the  aboral  piece  to  contract  refiexly  or 
perhaps  directly.  In  this  way,  therefore,  coordina- 
tion between  the  oral  and  aboral  piece  is  possible  in 
spite  of  the  interruption  of  the  nervous  connection. 
Friedlander  obtained  further  proof  of  this  by  divid- 
ing worms  completely  and  connecting  the  two  halves 
by  strings.  Even  then  he  found  that  the  aboral  piece 
moved  with  the  anterior  piece  in  a  perfectly  coordin- 
ated way.  These  facts  prove  that  the  brain  has  no 
leading  role  in  the  coordination  of  the  progressive 
motions  of  the  earthworm. 

What  part,  then,  does  the  central  nervous  system 
play  in  the  coordination  ?  It  serves  only  as  a  quick 
conductor  for  the  stimuli.  Friedlander  has  shown 
that  the  quick  motions  which  an  earthworm  shows 
upon  a  sudden  stimulus  are  no  longer  transmitted 
to  the  posterior  part  of  the  body  if  the  ganglion- 
chain  be  severed.  If  the  nervous  connection  be 
broken  so  that  stimuli  cannot  be  conducted  through 
the  nerves,  the  peripheral  structures  suffice  to  make 
coordinated  movement  possible. 

One  might  suppose  the  coordination  in  the  pro- 
gressive movements  of  higher  animals  to  be  of  an 
entirely  different  nature  from  that  of  worms.  An  ob- 
servation made  by  Goltz,  however,  shows  that  in 
dogs,  at  least,  this  is  not  the  case.  When  a  dog  with 
divided  spinal  cord  is  lifted  up  by  its  fore-legs,  so  that 
the  back  part  of  the  body  hangs  down  perpendicu- 
larly, a  remarkable  phenomenon  may  be  observed. 
The    hind-legs    perform    pendulum    motions    which 


EXPERIMENTS  ON  WORMS  87 

resemble  locomotion.  These  motions  are  presumably 
produced  by  the  passive  stretching  of  the  skin  on  the 
ventral  side  of  the  hip-joint  by  the  weight  of  the  legs. 
These  motions  are  comparable  to  the  reflex  contrac- 
tion of  the  longitudinal  muscles  of  the  earthworm, 
which  is  due  to  the  stretching  of  the  skin.  Because 
of  this  reflex,  coordinated  locomotion  would  be  quite 
possible  in  a  dog  with  divided  spinal  cord,  if  the  dog 
only  could  remain  standing  on  its  hind-legs.  The 
walking  movement  of  the  fore-legs  would  cause  the 
stretching  which  is  necessary  in  order  to  bring  about 
the  walking  movement  of  the  hind-legs.  The  differ- 
ence in  the  behaviour  of  a  dog  with  divided  spinal 
cord  and  of  an  earthworm  with  divided  ventral  nerve 
cord  in  regard  to  coordinated  progressive  movements, 
is  not  caused  so  much  by  differences  in  the  functions 
of  the  central  organs  as  by  differences  in  the  develop- 
ment of  the  peripheral  organs  of  the  skin  and  of  the 
organs  of  locomotion.  If  the  dog  had  short  stumps 
instead  of  its  long,  jointed  legs,  we  should  have,  after 
dividing  the  spinal  cord,  the  same  phenomenon  of 
progressive  movements  that  we  have  in  the  earth- 
worm. The  irritability  of  various  parts  of  the  peri- 
pheral organs  and  the  simple  segmental  arrangement 
of  the  nervous  elements  suffice  to  preserve  the  loco- 
motion when  it  has  once  been  started.  The  correct- 
ness of  this  conclusion  is  confirmed  by  experiments 
on  Nereis,  which  were  made  in  my  laboratory  by  S. 
S.  Maxwell  (5).  In  these  animals,  the  coordination 
of  the  movements  of  the  oral  and  aboral  pieces  is 


88     COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

practically  destroyed  by  dividing  the  ganglion  chain, 
for  the  deep  incisions  between  the  single  segments 
prevent  the  entire  cutaneous  muscle  layer  from  being 
stretched  equally.  The  structure  of  the  ventral  nerve- 
cord  in  Nereis  is  so  similar  to  that  of  Lumbricus  that 
we  should  not  be  justified  in  seeking  in  it  for  the 
conditions  which  cause  difference  of  behaviour.  In 
earthworms,  Maxwell  succeeded  in  confirming  Fried- 
lander's  observation.  I  obtained  similar,  although 
not  as  marked,  results  on  leeches  (2). 

If  an  earthworm  be  divided,  the  posterior,  brainless 
piece  continues  to  perform  progressive  movements. 
This  fact  confirms  the  opinion  that  the  brain  has  no 
controlling  part  in  progressive  movements. 

4.  The  question  now  arises.  Are  the  remaining  char- 
acteristic functions  of  the  earthworm  brain-functions 
or  segmental  functions  ?  If  we  place  Lumbricus  fceti- 
dus  in  a  transparent  closed  vessel,  the  animals  appear 
to  be  positively  stereotropic.  As  soon  as  they  reach 
an  angle  in  the  aquarium,  they  remain  there,  crawling 
along  where  the  glass  can  touch  them  on  two  sides. 
They  are  also  sensitive  to  the  differences  in  the  intens- 
ity of  light,  remaining  in  those  places  where  the 
light  is  weakest.  It  seems,  too,  when  one  or  more 
animals  settle  down  anywhere,  that  the  others  stop 
more  readily  in  that  place.  This  is  an  illustration  of 
"sociability"  among  lower  animals.  It  is  probably 
an  instance  of  chemotropic  irritability.  The  surface 
secretions  emanating  from  the  worm's  body  have  a 
quieting  influence  on  other  worms  of  the  same  kind ; 


EXPERIMENTS  ON  WORMS  89 

for  this  reason  they  become  quiet  when  in  contact 
with  a  worm  of  the  same  species.  These  chemical 
stimuli  act  as  a  trap,  just  as  the  comparative  minimum 
in  the  intensity  of  the  light  acts.  It  should  be  noted, 
in  this  connection,  that  when  animals  are  sensitive  to 
differences  in  the  intensity  of  light,  the  less  refractive 
rays  which  pass  through  red  glass  have  less  effect 
upon  them  than  the  more  refractive  rays  which  pass 
through  blue  glass.  The  earthworms  become  quiet 
under  red  glass  sooner  than  under  blue  glass. 

How  do  decapitated  earthworms  act  ?  Decapitated 
Lumbrici  foetidi  show  the  same  stereotropism  that 
normal  worms  show.  When  they  reach  the  concave 
angle  of  a  vessel,  they  have  no  inclination  to  leave  it 
again.  They  also  show  the  same  response  to  light. 
They  rest  in  those  places  where  the  intensity  of  the 
light  is  relatively  weakest,  and  they  move  when  the 
intensity  of  the  light  is  increased.  It  can  also  be 
shown  that  light  passing  through  blue  glass  acts  like 
light  of  greater  intensity,  while  light  passing  through 
red  glass  has  the  effect  of  light  of  weaker  intensity  (2). 

In  all  these  experiments  the  decapitated  pieces 
crawl  about  with  either  the  tail  or  the  anterior  end 
in  front. 

It  is  an  interesting  fact  that  the  reaction-time  when 
light  is  the  stimulus  is  not  appreciably  greater  in  de- 
capitated than  in  normal  earthworms.  The  animals 
used  for  the  experiment  were  in  a  box  in  which  they 
could  be  exposed  to  diffused  daylight  suddenly  with- 
out being  jarred.     In  from  three  to  eighteen  seconds 


90     COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

after  being  exposed  to  the  light,  the  decapitated  worms 
made  the  first  movements.  The  interval  was  about 
the  same  In  normal  worms. 

Ltimbrici  fostidi  live  In  the  decaying  compost  of 
stables,  and  probably  the  chemical  nature  of  certain 
substances  contained  In  the  compost  holds  them 
there.  When  one-half  of  the  bottom  of  the  box  is 
covered  with  moist  white  blotting-paper,  the  other 
half  with  a  thin  layer  of  compost,  all  the  normal  worms 
that  are  placed  on  the  paper  soon  gather  on  the  com- 
post. The  aboral  pieces  of  divided  worms  behave  in 
the  same  way.  When  placed  upon  the  blotting-paper, 
they  are  not  attracted  directly  by  the  odours  of  the 
compost,  but  as  soon  as  they  come  In  contact  with  It 
in  moving  about,  they  crawl  on  It  and  do  not  leave  It 
again.  After  a  short  time  all  the  brainless  worms  are 
on  the  compost.  When  placed  on  a  heap  of  compost, 
most  of  them  crawl  into  it  within  a  short  time.  This 
is  not  due  solely  to  the  light,  as  the  same  reaction 
also  takes  place  in  the  dark  (2). 

Thus  we  see  that  in  decapitated  earthworms  all  the 
reactions  shown  by  the  normal  worms  are  retained. 
Hence  the  brain  (supraoesophageal  ganglion)  has  in 
this  case  no  leading  r6le. 

We  cannot  be  too  careful  in  drawing  conclusions 
in  regard  to  the  principal  function  of  a  ganglion. 
Nereis,  a  much  more  highly  developed  Annelid  than 
the  earthworm,  burrows  in  the  sand ;  if  decapitated, 
this  function  ceases.  One  might  suspect  that  this  was 
due  to  the  loss  of  the  brain,  but  such  Is  not  the  case. 


EXPERIMENTS  ON  WORMS  91 

Earlier  experiments  had  led  me  to  suspect  that  the 
"  spontaneous  "  or  "  instinctive"  burrowing  was  only 
a  reflex  produced  by  the  contact-stimuli  of  the  sand. 
I  then  attempted  to  find  out  whether  it  were  not  pos- 
sible under  special  conditions  to  produce  the  same 
reflex  in  brainless  pieces.  I  placed  such  a  piece  of  a 
Nereis  on  the  sand  ;  as  usual  it  remained  quiet.  I 
then  gradually  covered  the  forward  end  with  sand. 
The  rest  of  the  animal  immediately  began  to  make 
the  typical  movements  which  the  animal  makes  in 
forcing  Its  way  into  the  sand.  At  the  same  time  the 
glands  began  to  secrete  the  sticky  substance  which 
cements  the  particles  of  sand  together,  forming  the 
wall  of  the  burrow-hole.  This  secretion-phenomenon 
regularly  accompanies  the  burrowing  of  these  animals  ; 
it  is  the  same  secretion  that  in  other  animals  leads  to 
the  formation  of  a  case. 

But  why  does  the  Nereis  not  burrow  when  deprived 
of  its  brain  ?  For  the  simple  reason  that  it  makes 
use  of  the  organs  of  the  mouth  in  burrowing,  and  these 
are  amputated  with  the  head.  Hence  it  is  the  loss  of 
a  peripheral  head-organ  which  keeps  the  decapitated 
Nereis  from  burrowing,  and  not  the  loss  of  the  brain. 
The  brain  in  this  case  merely  performs  the  function 
of  a  segmental  ganglion — that  is,  it  acts  as  the  ganglion 
of  that  segment  to  which  the  peripheral  head-organ 
belongs. 

5.  We  will  now  turn  our  attention  to  the  brain- 
functions  of  Nereis. 

After  a  Nereis  has  burrowed  in  the  sand  it  lives  in 


92     COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

the  same  case  for  a  long  time.  If  the  supraoesopha- 
geal  ganglion  (o,  Fig.  26)  be  removed,  the  animal  be- 
comes restless,  as  S.  S.  Maxwell  has  found.  It  crawls 
about  on  the  sand  unceasingly,  making  no  attempt  to 
burrow.  This  restlessness  is  marked  by  one  feature 
which  we  find  in  higher  animals  after  certain  injuries 
to  the  brain  —  namely,  the  Nereis  does  not  withdraw 
from  obstacles  but  attempts  to  force  its  way  through 
them. 

If  normal  Nereis  are  in  a  square  aquarium  the  bot- 
tom of  which  is  covered  with  sand,  they  will  crawl 
about,  if  undisturbed,  on  the  sides  of  the  glass.  This 
is  the  result  of  stereotropism.  A  Nereis  that  has  lost 
the  supraoesophageal  ganglion  will  behave  in  the 
same  way,  except  that  when  it  reaches  a  corner  it 
does  not  turn  out  but  attempts  to  go  through  the 
glass.  If  there  are  several  animals  which  have  been 
operated  upon  in  a  vessel,  they  will  assume  the  po- 
sition represented  in  Fig.  29.  The  worms  remained 
like  this  for  many  hours  at  a  time,  and  then  died  in 
consequence  of  their  vain  attempt  to  go  forward. 
Those  reactions  are  wanting  which  in  the  normal 
Nereis  result  from  the  application  of  contact-stimuli 
to  the  oral  end.  The  reader  who  is  familiar  with 
brain-physiology  may  already  have  been  reminded  in 
this  connection  of  the  dogs  from  which  Goltz  re- 
moved the  anterior  half  of  the  cerebral  hemispheres. 

If  glass  tubes  20  cm.  long,  with  a  bore  a  little 
larger  than  the  diameter  of  the  worm,  are  placed  in 
an  aquarium   without  sand,  the  normal  Nereis  will 


EXPERIMENTS  ON  WORMS 


93 


crawl  into  them  and  will  not  leave  them  again.  This 
is  due  to  stereotropism.  If  there  are,  for  instance, 
six  such  tubes  in  a  vessel  and  six  normal  Nereis  are 
put  into  it,  we  may  be  sure  that  after  a  few  hours 
every  Nereis  will  have  established  itself  in  a  tube.     It 


I 


\ 


Fig.  29.  A  Group  of  Nereis  whose  Brains  have  been  Removed.  They  at 
LAST  Collect  in  a  Corner  of  the  Aquarium  and  Perish  in  their  Vain 
Attempt  to  Go  through  the  Glass.     (After  Maxwell.) 

frequently  occurs  that  a  Nereis  goes  into  a  tube  that 
already  has  an  occupant.  In  that  case  the  new-comer 
withdraws  with  a  start  as  soon  as  it  touches  the  old 
occupant.  As  long  as  the  new-comer  is  in  pos- 
session of  its   brain,  it  leaves  the  tube  under  such 


94     COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

circumstances,  but  if  it  has  lost  the  supraoesophageal 
ganghon,  the  presence  of  the  other  worm  in  the  tube 
has  no  inhibitory  effect.  It  tries  to  force  its  way  into 
the  tube  even  if  it  perishes  in  the  attempt.  If  both 
worms  have  lost  the  supraoesophageal  ganglion,  they 
rub  their  heads  together  until  they  are  sore.  If  we 
wish  to  keep  them  alive,  they  must  be  separated  by 
breaking  the  tube.  If  we  compare  the  conduct  of  a 
Nereis  whose  brain  has  been  amputated,  with  that  of 
a  normal  worm,  the  difference  seems  to  be  of  the 
same  nature  as  that  between  an  insane  and  a  rational 
human  being.  It  would  be  erroneous,  however,  to 
conclude  that  the  normal,  brain-endowed  Nereis  pos- 
sesses reason  or  intelligence.  The  peculiar  irritability 
by  means  of  which  the  Nereis  draws  its  head  back  and 
moves  backward  out  of  the  tube  depends  upon  organs 
which  are  located  in  the  forward  end  of  the  body  and 
whose  sensory  nerves  go  to  the  supraoesophageal 
ganglion.  Hence,  if  the  supraoesophageal  ganglion 
is  extirpated,  the  connection  between  these  organs 
and  the  rest  of  the  body  is  interrupted,  and  the  stimuli 
which  affect  the  forward  part  of  the  body  can  no 
longer  produce  backward  movements  in  the  posterior 
portion  of  the  animal. 

This  does  not,  however,  explain  the  change  of 
character,  the  restlessness  of  the  Nereis  which  has 
been  deprived  of  its  brain.  It  is  maintained  that,  if 
the  spontaneous  activity  or  the  reflex  irritability  of 
an  animal  is  increased  after  the  loss  of  a  part  of  the 
brain,  that  part  is  an  inhibitory  mechanism.     Nothing 


EXPERIMENTS  ON  WORMS  95 

is  gained,  however,  by  making  such  a  statement.  We 
wish  to  know  how  the  supraoesophageal  gangHon  can 
inhibit  movements,  and  how  its  absence  can  increase 
spontaneity. 

It  is  not  possible  to  offer  at  present  more  than  a 
suggestion.  We  can  increase  and  decrease  the  loco- 
motor activity  of  a  jelly-fish  at  desire  by  changing 
the  constitution  of  the  sea-water.  If  we  increase  the 
number  of  Na  ions  in  the  sea-water,  the  rate  of  rhyth- 
mical contractions  in  Gonionemus  increases  and  the 
animal  becomes  restless.  If  the  number  of  Ca  ions 
be  increased,  the  animal  becomes  quiet.  It  is,  more- 
over, a  fact  that  the  different  parts  of  a  Gonionemus 
are  affected  somewhat  differently  by  the  same  ions, 
inasmuch  as  the  margin  is  more  immune  against  the 
effects  of  Ca  ions  than  the  centre.  I  think  it  possible 
that  there  is  a  similar  difference  between  the  segments 
belonging  to  the  supraoesophageal  and  suboesopha- 
geal  ganglion.  It  might  be  possible  that  the  ions 
(or  some  other  substance)  of  the  blood  influence  the 
supraoesophageal  ganglion  or  its  segments  in  such  a 
way  as  to  cause  a  decrease  in  the  locomotions,  while 
the  Game  constituents  of  the  blood  do  not  have  such 
an  effect  upon  the  subcesophageal  ganglion  or  its 
segment.  But  the  blood  is  not  the  only  agency 
which  is  to  be  considered  in  this  connection.  The 
supraoesophageal  ganglion  of  Annelids  is  connected 
with  the  alimentary  canal  by  nerves.  The  processes 
which  go  on  in  the  intestine — that  is,  the  chemical  pro- 
cesses of  secretion  and  digestion — can  only  affect  the 


96     COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

whole  animal  nervously  as  long  as  the  supraoesopha- 
geal  ganglion  Is  Intact.  If  It  Is  removed,  the  whole 
Influence  of  this  so-called  sympathetic  nervous  system 
ceases.  It  is  possible  that  the  stimuli  which  pass 
from  the  sympathetic  Into  the  central  nervous  system 
may  condition  the  alternation  of  rest  and  activity 
which  characterises  the  normal  animal,  and  that  the 
removal  of  this  stimulation  may  remove  the  necessity 
of  resting. 

Maxwell  has  found  that  a  Nereis  which  has  lost  the 
subcesophageal  ganglion  becomes  quiet.  Such  ani- 
mals make  no  attempt  at  burrowing.  The  reason  for 
this  Is  that  the  motor  nerves  of  the  oesophageal  mus- 
cles originate  in  the  subcesophageal  ganglion,  so  that 
removal  of  this  ganglion  causes  paresis  or  paralysis  of 
these  muscles.  The  pharynx  plays  a  great  r6le  In  bor- 
ing the  hole.  It  Is  due  to  this  same  paralysis  or  paresis 
of  the  oesophageal  muscles  that  a  Nereis  no  longer 
eats  after  losing  the  subcesophageal  ganglion  (5). 

We  wish  to  mention  here,  however,  that  removal 
of  the  subcesophageal  ganglion  does  not  bring  about 
disturbances  In  taking  up  food  In  all  Annelids.  Max- 
well found  that  the  leech  Is  still  able  to  suck  itself  full 
of  blood  after  losing  the  ganglion.  McCaskill  dis- 
covered, however,  that  in  the  leech  the  motor  nerves 
of  the  sucking  apparatus  originate  in  the  supra- 
cesophageal  ganglion.  The  subcesophageal  ganglion  in 
the  leech  behaves  like  the  first  link  In  the  ganglion- 
chain. 

As  regards  the  restlessness  of  Nereis  after  removal 


EXPERIMENTS  ON  WORMS  97 

of  the  supraoesophageal  ganglion  and  the  repose  after 
the  removal  of  the  suboesophageal  ganglion,  we  wish 
to  emphasise  the  fact  that  they  have  nothing  to  do 
with  the  wound.  Maxwell's  observations  were  made 
on  animals  whose  wounds  were  healed.  If  we  make 
a  wound  like  that  made  in  removing  the  ganglion, 
only  with  the  difference  that  the  ganglion  is  left  intact, 
none  of  the  above-mentioned  disturbances  occur. 
Immediately  after  the  operation  the  worm  burrows 
again  in  spite  of  the  wound. 

Differences  like  those  found  between  the  behaviour 
of  normal  Nereis  and  of  Nereis  from  which  the  brain 
has  been  removed  do  not  appear  in  earthworms  under 
the  same  conditions.  What  causes  this  difference? 
Is  the  supraoesophageal  ganglion  in  the  earthworm 
a  segmental  ganglion,  while  in  Nereis  it  is  a  "control- 
ling ganglion,"  a  brain  in  the  sense  of  the  anthropo- 
morphic nerve-physiology  ? 

I  am  inclined  to  believe  that  we  have  to  deal  with 
differences  of  the  same  character  as  those  found 
between  Acalephse  and  Hydromedusse.  In  addition 
it  should  be  said  that  there  is  a  much  higher  degree 
of  differentiation  of  the  head-organs  in  Nereis  than  in 
the  earthworm.  We  have  already  seen  in  preceding 
chapters  that  the  apparent  functions  of  the  brain  or  of 
the  ganglia  are  chiefly  determined  by  the  peripheral 
organs.  In  Nereis  the  differentiation  of  the  head- 
segments  is  carried  much  farther  than  that  of  the 
other  segments  (Fig.  30).  In  the  earthworm,  on  the 
other  hand,  the  difference  is  much  less  (Fig.  2  7). 


98     COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 


In  Vertebrates  the  head  contains  special  sense- 
organs,  mouth-organs,  which  are  lacking  in  the  other 
segments.  In  judging  of  the  relation  of  the  brain- 
ganglia  to  the  other  segmental  ganglia  of  the  body 
this  fact  should  not  be  overlooked.  Not  infrequently 
physiologists  have    ascribed   to  a  ganglion  what  in 

reality  was  due  to  the 
higher  differentiation  of 
the  peripheral  organs  of 
the  segment. 

We  desire  now  to 
touch  briefly  upon  the 
behaviour  of  the  muscles 
after  extirpation  of  the 
ganglion,  for  the  phe- 
nomena will  occupy  our 
attention  repeatedly. 

In  the  case  of  loss  or 
a  congenital  lack  of  a 
piece  of  the  spinal  cord, 
the  skeletal  muscles  belonging  to  the  corresponding 
segment  atrophy.  Nothing  of  the  kind  occurs  in 
leeches  or  earthworms  from  whose  ventral  chain 
a  piece  has  been  removed.  I  believe  that  the  dif- 
ference is  determined  as  follows  :  In  worms  direct 
impulses  flow  from  the  neighbouring  muscles  to  the 
muscles  that  have  been  deprived  of  their  ganglion, 
while  in  Vertebrates,  as  soon  as  the  spinal  cord  is 
destroyed,  the  protoplasmic  connection  between  the 
skeletal  muscles  and  the  rest  of  the  body  is  destroyed 


Fig.   30. 


Head  of  Nereis. 
Quatrefages.) 


(After 


EXPERIMENTS  ON  WORMS  99 

and  it  is  not  possible  for  stimuli  to  be  transmitted. 
In  the  muscles  of  the  blood-vessels  of  the  Vertebrates, 
however,  a  conduction  of  the  stimulation  from  element 
to  element  is  possible.  For  this  reason  their  reactions 
remain  intact  even  in  higher  animals  after  destruction 
of  the  corresponding  segments  of  the  spinal  cord. 
In  Nereis,  after  division  of  the  ganglion-chain,  a 
phenomenon  may  be  observed  that  reminds  one  of 
the  Brondgeestian  phenomenon.  The  back  part  of 
the  body  becomes  more  flat,  while  the  part  that  is 
connected  with  the  brain  remains  round.  This  indi- 
cates a  relaxation  of  the  ring-muscles  in  the  part  of 
the  animal  that  is  situated  behind  the  point  of 
division. 

The  results  of  our  physiological  analysis  of  the 
functions  of  the  central  nervous  system  in  Annelids  are 
in  perfect  harmony  with  Professor  C.  O.  Whitman's 
investigations  on  the  morphological  structure  of  the 
central  nervous  system  in  Annelids.  He  arrives  at  the 
conclusion  that  the  brain  of  Annelids  is  not  of  a  higher 
order  than  the  other  segmental  ganglia  (7). 

Bibliography. 

1.  Lang,  A.  Untersuchungen  zur  vergleichenden  Anatomie  und 
Histologic  des  Nervensystems  der  Plathelminthen.  Mittheil.  aus  der 
Zoolog.     Station  zu  Neapel^  Bd.  I. 

2.  LoEB,  J.  Beitrdge  zur  Gehirnphysiologie  der  Wurmer^ 
Pfluger's  Archiv,  Bd.  56,  1894  ;  and  Ueber  kUnstliche  Umwand- 
lung  positiv  helistropischer  Thiere  in  negativ  helioiropische  und  um- 

\gekehrt,  Pfliigers  Archiv,  Bd.  54,  1893. 

3.  Graber.     Grundlinien  zur  Erforschung  des  Helligkeits-und 


loo  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

Farbensinns  der  Thiere.      Prag  und  Leipzig,  1884.     Verlag  von 
Tempsky  &  Freitag. 

4.  Friedlander,  Benedict.  Ueber  das  Kriechen  der  Regen- 
wiirmer^  Biologisches  Centralblatt^  Bd.  8  ;  and  Zur  Beurtheilung 
und  Erforschung  der  thierischen  Bewegungen^  Biolog.  Centralblatt, 
Bd.  II ;  and  Beitrdge  zur  Physiologie  des  Centralnervensy stems  und 
des  Bewegungsmechanismus  der  Regenwurmer^  Pfluger*s  ArchiVy  Bd. 

58- 

5.  Maxwell,  S.  S.  Beitrdge  zur  Gehirnphysiologie  der  An- 
neliden.     Pflilger's  Archiv^  Bd.  67,  1897. 

6.  VAN  DuYNE,  John.  Ueber  Heteromorphose  bei  Planarien. 
Pflilger's  ArchiVy  Bd.  64,  1897. 

7.  Whitman,  C.  O.  The  Metamerism  of  Clepsine.  Festschrift 
fur  Leuckart,  Leipzig,  1892. 


CHAPTER  VII 

EXPERIMENTS  ON  ARTHROPODS 

I.  Experiments  on  the  lowest  animal  forms  have 
taught  us  that  the  peculiar  reactions  of  animals  are 
determined,  first,  by  the  different  forms  of  irrita- 
bility of  the  elements  composing  the  tissues,  and, 
second,  by  the  arrangement  of  the  muscle-fibres. 
The  central  nervous  system  does  not  control  response 
to  stimulation :  it  merely  serves  as  a  conductor  from 
the  point  of  stimulation  to  the  muscle  through  which 
weaker  stimuli  may  pass,  and  pass  more  rapidly  than 
would  be  possible  if  the  muscle  were  stimulated 
directly. 

In  the  Annelids  each  ganglion  is  the  relay  station 
for  the  sensory  and  motor  nerves  of  the  correspond- 
ing segment.  If  the  head  exercises  a  stronger  in- 
fluence upon  the  behaviour  of  the  animal  than  any 
other  segment,  as  in  Nereis,  for  instance,  I  believe 
it  is  due  to  the  fact  that  in  the  oral  end  more  kinds 
of  irritability  are  present  and  more  peripheral  organs 
are  differentiated  (sense-organs,  mouth,  etc.)  than  in 
the  other  segments.  The  fact  that  in  this  case  the 
sympathetic  nervous  system  takes  its  origin  from  the 

lOI 


I02  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

supraoesophageal  ganglion  also  helps  to  increase 
the  predominance  of  the  head-segments.  Hence  it 
is  not  the  presence  of  the  supraoesophageal  ganglion 
which  determines  the  greater  number  of  reactions 
and  their  more  complicated  nature  in  the  oral  seg- 
ments of  some  Annelids,  but  it  is  the  presence  of  the 
greater  number  of  irritabilities  and  the  greater  number 
of  specific  organs  in  the  forward  end  of  the  body.  In 
addition  there  may  exist  chemical  differences  between 
the  various  segments  of  an  animal. 

We  shall  now  see  that  this  conception  of  the 
central  nervous  system  also  holds  good  for  the  Ar- 
thropods. We  will  begin  the  analysis  of  the  brain- 
functions  of  these  forms  with  Limulus  polyphemus 

(Fig-  30- 

Zoologists  maintain  that  Limulus  is  a  very  old  form. 

If  tenacity  of  life  favours  the  age  of  the  species  as  it 
does  the  age  of  individuals,  this  assertion  can  be  readily 
understood,  for  it  is  difficult  to  conceive  of  a  tougher 
animal.  At  my  suggestion.  Miss  Ida  Hyde  made  ex- 
periments on  the  functions  of  the  single  parts  of  the 
central  nervous  system  of  Limulus  polyphemus,  with 
special  attention  to  the  respiratory  centres  (i).  Con- 
cerning these  centres,  Faivre  had  made  assertions 
which  did  not  harmonise  with  the  apparent  segmental 
arrangement  of  the  central  nervous  system.  He  as- 
sumes that  the  suboesophageal  ganglion  which  is 
located  in  the  head  has  a  coordinating  influence 
on  the  respiratory  movements,  but  in  forms  like  these 
with  the  respiratory  organs  (gills)  in  the  abdomen, 


EXPERIMENTS  ON  ARTHROPODS 


103 


the  respiratory  nerves  must  originate  In  the  abdomi- 
nal ganglion-chain.    The  conditions  existing  in  Verte- 


\ 


I.Afri. 


fl.  AU 

III.AU 


Fig.  31. 


LiMULUS  Polyphemus  with  the  Central  Nervous 

System  Exposed. 


Oy  supraoesophageal  ganglion;  c,  commissure;  «,  suboesophageal ganglion ;  I-IV{V  and 
yi  Abd.\  abdominal  ganglia  of  the  respiratory  segments. 

brates  evidently  gave  rise  to  the  idea  of  a  coordinating 
ganglion  located   in  the  head.     In  Vertebrates  the 


I04    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

diaphragm,  the  chief  respiratory  muscle,  is  far  sepa- 
rated from  its  nervous  segment,  but  this  is  due  merely 
to  a  shifting  during  development.  The  Anlage  is 
really  located  near  the  head.  Such  displacements 
during  growth  do  not  take  place  to  this  extent  in 
Arthropods.  Faivre  seems  to  have  been  entirely 
under  the  influence  of  current  views  of  Vertebrate 
physiology,  especially  those  of  Flourens,  and  so  he 
was  led  into  making  incorrect  statements  regarding 
the  physiology  of  the  Invertebrates. 

The  central  nervous  system  of  LImulus  consists  of 
the  following  parts  (Fig.  31)  :  A  supracesophageal 
ganglion  0,  which  Is  usually  called  the  brain,  an 
oesophageal  ring  {c,  Fig.  31)  which  encloses  the  oe- 
sophagus and  consists  of  fibres  and  ganglia,  a  sub- 
oesophageal  ganglion  u,  and  the  ventral  chain  with  six 
abdominal  ganglia.  These  parts  send  out  a  series 
of  peripheral  nerves.  In  LImulus  the  situation  of 
the  nerve-centres  is  schematically  developed  :  every 
peripheral  organ  has  Its  nerve-centre  in  that  part 
of  the  nervous  system  which  belongs  to  its  segment. 
Perhaps  this  can  be  best  seen  from  the  following  ex- 
periment made  by  Miss  Hyde  :  The  whole  central 
nervous  system  of  a  LImulus  was  removed  with  the 
exception  of  a  little  piece  of  the  oesophagus-ring  {c. 
Fig.  31)  and  the  abdominal  ganglia  (I-VI  Abd,  Fig. 
31).  No  connection  remained  between  these  two 
pieces.  The  piece  of  the  oesophageal  ring  lay  at  the 
same  height  with  the  three  mouth-appendages  that 
are  used  for  taking  in  food.      These  three  mouth- 


EXPERIMENTS  ON  ARTHROPODS  105 

appendages  retained  their  function,  and  eating  move- 
ments were  performed  reflexly  when  meat  was  placed 
on  the  appendages.  The  rest  of  the  appendages 
were  entirely  paralysed,  with  the  exception  of  the 
gills  on  the  ventral  side  of  the  abdomen.  The  animal 
was  reduced  to  a  mere  eating  and  breathing  machine. 
It  was  fed  artificially  and  so  kept  alive. 

Patten  has  shown  further  that  each  feeding-appen- 
dage continues  to  take  food  normally  and  carries  it 
to  the  mouth  if  the  piece  of  the  oesophagus-ring 
from  which  its  nerves  take  their  origin  is  preserved. 
These  feeding-appendages  discriminate  the  chemical 
and  tactile  nature  of  the  food  that  is  offered  them, 
just  as  the  tentacles  of  the  Actinians  do — they  refuse 
to  accept  it  unless  the  substances  offered  fulfil  cer- 
tain chemical  and  mechanical  conditions.  As  regards 
the  conception  of  these  phenomena  and  their  mechan- 
ics, no  difference,  of  course,  exists  between  the  be- 
haviour of  the  tentacles  of  the  Actinians  and  the 
behaviour  of  the  mouth-appendages  of  the  Limuli  ex- 
cept that  determined  by  the  skeletal  relations. 

If  we  remove  one  half  (for  instance,  the  right  half) 
of  the  supraoesophageal  ganglion  in  Limulus  {0,  Fig. 
31),  the  animal  usually  moves  no  longer  straight 
ahead,  but  in  a  circle  with  more  or  less  of  a  curvature 
toward  the  uninjured  (left)  side.  This  is  an  instance 
of  the  well-known  circus-motions.  We  shall  return 
to  the  mechanics  of  such  motions  in  a  later  chapter. 

If  the  whole  supraoesophageal  ganglion  be  re- 
moved, the  animal  is  able  to  take  food  placed  upon 


io6    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

the  mouth-organs,  but  loses  its  spontaneity  in  so  far 
as  this  is  expressed  by  progressive  movements.  It 
will  even  retain  abnormal  postures  in  which  it  is 
placed.  The  operations  were  performed  during  the 
period  of  heat.  Male  Limuli  that  had  lost  the  supra- 
oesophageal  ganglion  no  longer  noticed  the  females. 
On  the  other  hand,  the  legs  attempted  to  remove  an 
irritating  object  from  the  surface  of  the  body.  De- 
capitated frogs  act  in  the  same  way. 

In  the  cases  mentioned  above,  the  Limuli  had  en- 
dured the  operation  well  and  their  wounds  were 
entirely  healed.  If  the  oesophageal  commissure  {c. 
Fig.  31)  be  severed  on  one  side,  circus-movements 
will  appear  in  the  direction  of  the  injured  side,  but 
these  only  last  until  the  wound  is  healed.  The  circus- 
motions  which  ensue  upon  extirpation  of  one-half  of 
the  brain  also  disappear  after  a  time.  If  ganglia  be 
removed  from  the  oesophagus-ring,  the  appendages 
corresponding  to  the  extirpated  ganglia  are  perma- 
nently paralysed. 

2.  After  extirpation  of  the  subcesophageal  ganglion 
(u.  Fig.  31)  the  animal  remains  extremely  quiet,  and 
often  lies  on  the  same  spot  for  days.  But  its  respira- 
tion continues  normal,  and  this  proves  the  erroneous- 
ness  of  Faivre's  opposed  assertion.  Except  for  its 
immobility  and  the  fact  that  the  extensors  of  the 
joint  between  the  thorax  and  abdomen  are  paralysed 
as  a  result  of  nerve-injuries,  the  animal  appears 
normal. 

The  four  or  six  ganglia  of  the  abdomen  (Fig.  31) 


EXPERIMENTS  ON  ARTHROPODS  107 

innervate  the  five  gills  which  are  located  on  the 
abdomen  of  the  animal.  If  the  whole  central  nervous 
system  with  the  exception  of  these  ganglia  be  removed, 
the  rhythmical  respiratory  activity  continues  un- 
changed. Immediately  after  the  operation,  which  is 
accompanied  by  a  great  loss  of  blood,  the  respiration 
may  be  interrupted  for  an  hour  or  more.  If  we  touch 
the  gill-plates  during  this  time,  the  stimulation  occa- 
sions a  series  of  rhythmical  respiratory  movements 
which,  however,  soon  cease.  After  a  time,  the  gills 
begin  their  respiratory  activity  again  spontaneously, 
and  are  only  interrupted  by  an  occasional  cramp. 
This  interruption  of  the  respiratory  movements  is  also 
found  occasionally  in  the  normal  Limulus,  where,  if  it 
remains  quiet,  the  respiratory  movements  may  cease 
for  an  hour  or  more.  At  this  place  we  will  not  go 
into  details  concerning  this  phenomenon. 

The  abdominal  ganglia  are  thus  centres  for  the 
automatic  movements  of  the  abdominal  gill-plates. 
All  the  gills  move  in  the  same  phase.  It  is  probable 
that  the  inspiration  begins  with  the  first  gill  and  ex- 
tends to  the  following  gills  in  succession,  but  rapidly 
enough  to  make  the  whole  appear  simultaneous.  Ac- 
cording to  the  prevailing  opinions,  we  should  be 
obliged  to  assume  from  this  either  that  only  one,  for 
instance  the  first,  of  the  four  abdominal  ganglia,  is 
automatically  active,  and  that  the  rest  are  stimulated 
from  this,  or  that,  if  each  of  the  four  ganglia  is 
rhythmically  active,  a  common  centre  of  coordination 
exists  somewhere  in  the  four  ganglia.     If  we  sever 


io8    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

the  ventral  cord  between  two  ganglia,  for  instance 
between  the  second  and  third,  we  find  that  in  spite  of 
the  division  all  the  gills  continue  to  breathe.  Any 
ganglion  may  be  entirely  isolated — that  is,  the  commis- 
sure before  and  behind  it  may  be  severed,  and  the 
corresponding  gill  continue  to  make  respiratory 
motions.  This  proves  that  every  ganglion  is  the  seat 
of  an  automatic  periodic  activity.  But  how  does  it 
happen  that  all  the  gills  move  simultaneously  as  long 
as  their  ganglia  are  connected  ?  The  number  of  the 
respirations  produced  is  the  same  even  when  the 
abdominal  ganglia  are  isolated.  This  is  probably  due 
to  the  fact  that  the  number  of  respirations  is  de- 
termined by  the  temperature  and  the  chemical  nature 
of  the  blood.  The  amount  of  carbon  dioxide  and 
certain  other  substances,  especially  those  formed  in 
the  muscles  (Zuntz  and  Geppert),  controls  the  number 
of  respirations.  The  phase  of  the  movement,  on  the 
other  hand,  is  not  the  same  in  the  various  segments 
where  the  ganglia  are  isolated.  The  gills  that  are 
situated  anterior  to  the  place  of  incision  may  be  in- 
spiring while  those  behind  the  incision  are  expiring. 
These  phenomena  lead  me  to  believe  that  in  the  nor- 
mal animal  coordination  is  regulated  in  the  same  way 
that  it  is  regulated  in  the  activity  of  the  heart  and  in  the 
movements  of  Medusae.  The  ganglion  that  acts  first, 
that  is  to  say,  the  ganglion  that  acts  quickest,  stimulates 
those  connected  with  it  nervously  and  so  determines 
the  correspondence  of  phase.  This  view  is  supported 
by  the  fact  that  no  matter  how  the  ganglia  may  be 


EXPERIMENTS  ON  ARTHROPODS  109 

separated  from  each  other,  those  that  are  connected 
nervously  always  keep  their  gills  in  the  same  phase  of 
activity.  Were  there  a  centre  of  coordination  in  any 
ganglion,  a  group  of  ganglia  separated  from  this  centre 
would  be  active  in  an  uncoordinated  manner,  but 
such  is  never  the  case. 

3.  In  higher  animals,  the  conditions  controlling  re- 
spiration scarcely  differ  from  those  in  Limulus.  There 
is  a  series  of  segmental  ganglia  in  the  thoracic  portion 
of  the  spinal  cord  which  sends  nerves  to  the  thoracic 
respiratory  muscles  of  the  respective  segments.  These 
ganglia  extend  into  the  cervical  portion  of  the  spinal 
cord,  and  the  fourth,  third,  and  fifth  pairs  of  spinal 
nerves  give  rise  to  the  fibres  of  the  phrenic  nerve 
which  goes  to  the  diaphragm.  The  diaphragm  in 
reality  belongs  to  the  corresponding  segments  of  the 
neck  portion,  and  has  attained  its  present  position  only 
through  a  shifting  of  position  during  growth.  One 
would  expect  in  text-books  of  physiology  to  find  the 
phenomena  of  respiration  explained  as  follows : 
Chemical  changes  which  are  continually  going  on  in 
the  body,  or  in  these  segmental  ganglia,  under  the 
influence  of  heat  (the  temperature  of  the  body),  pro- 
duce a  periodic  activity  in  these  ganglia  and  conse- 
quently in  the  respiratory  muscles.  The  segmental 
connection  existing  between  the  ganglia  and  the 
muscles  would  bring  about  coordination  just  as  it 
does  in  Limulus.  But  in  the  majority  of  text-books 
we  find  statements  of  the  following  character  :  The 
automatic  activity  of  the  respiratory  muscles  is  pro- 


no    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

duced  much  higher  up,  at  a  certain  point  of  the 
medulla  oblongata  near  the  place  where  the  vagus 
enters,  which  Flourens  called  the  noeud  vital.  This 
place  is  supposed  to  be  the  respiratory  centre.  This 
view  is  justified  by  two  facts  :  first,  the  destruction  of 
the  nceud  vital  causes  a  cessation  of  respiration ; 
and,  second,  severing  the  spinal  cord  between  the 
noeud  vital  and  the  origin  of  the  phrenic  nerve  like- 
wise causes  respiration  to  cease.  These  facts  do 
not  justify  the  conclusion  that  Le  Gallois,  Flourens, 
and  with  him  the  majority  of  modern  physiologists, 
have  drawn  —  namely,  that  the  automatic  activity  of 
respiration  is  located  not  in  the  segmental  ganglia,  but 
higher  up  in  the  noeud  vital.  We  should  have  just  as 
much  right  to  assume  that  in  Limulus  the  rhythmical 
respiratory  activity  was  produced  higher  up,  in  the 
suboesophageal  ganglion  for  instance,  for  in  this  animal, 
too,  respiration  ceases  for  a  time  immediately  after  the 
removal  of  the  suboesophageal  ganglion.  We  have 
seen  in  this  case,  however,  that  the  cessation  is  only 
temporary,  and  is  due  to  the  shock,  for  respiratory 
activity  can  go  on  again  even  when  the  whole  central 
nervous  system,  with  the  exception  of  the  abdominal 
ganglia,  has  been  removed.  Neither  is  the  cessation 
of  respiration  in  Vertebrates  permanent  after  removal 
of  the  noeud  vital  or  division  of  the  spinal  cord  be- 
tween the  noeud  vital  and  the  third  cervical  vertebra. 
Langendorff  has  made  the  important  discovery  that 
decapitated  Vertebrates  which  have  lost  the  noeud 
vital  are  still  able  to  perform  independent  respiratory 


EXPERIMENTS  ON  AR  THRO  PODS  1 1 1 

movements  (2).  It  was  necessary  to  make  these  exper- 
iments on  young  or  new-born  Vertebrates,  as  on  them 
the  effect  of  the  shock  does  not  last  so  long.  If  one 
succeeds  in  keeping  these  animals  alive  by  introducing 
artificial  respiration  until  the  effect  of  the  shock  result- 
ing from  the  operation  has  passed  off,  spontaneous 
respiration  begins  again.  I  consider  it  possible  that, 
if  we  could  keep  an  adult  Vertebrate  alive  without  the 
noeud  vital  for  some  time,  the  respiratory  motions 
would  be  resumed  again.  But  why  does  respiration 
stop  temporarily  after  the  isolation  of  the  segmental  re- 
spiratory ganglia  from  the  higher  parts  of  the  central 
nervous  system  ?  An  answer  to  this  question  would  be 
in  part  an  explanation  of  the  mystery  of  the  shock- 
effects.  It  might  be  possible  that  something  has  to  be 
supplied  constantly  by  certain  nerve-elements  in  the 
subcesophageal  ganglion  or  the  medulla  to  the  seg- 
mental respiratory  ganglia,  which  enables  the  latter  to 
be  active  automatically.  In  destroying  the  noeud  vital 
we  perhaps  destroy  the  pathway  along  which  these 
constant  impulses  are  carried  to  the  segmental  re- 
spiratory ganglia  in  the  spinal  cord.  But  where  do 
these  impulses  come  from  and  what  is  their  character  ? 
In  watching  the  respiratory  motions  of  a  Limulus,  I 
received  the  impression  that  the  operculum  always 
moves  first,  and  that  the  respiratory  motions  of  the 
lower  segments  follow  successively.  In  the  lower 
Vertebrates,  e.  g,  the  frog,  we  have  a  mouth  respir- 
ation, whose  segmental  ganglia  are  situated  in  the 
medulla.     Likewise  the  segmental   ganglia   for   the 


112     COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

respiratory  activity  of  the  gills  in  fish  are  situated  in 
the  medulla.  Could  it  not  be  possible  that  in  Mam- 
malians the  segmental  ganglia  for  the  gill-respiration 
continue  to  be  active,  although  the  gills  or  the  oral 
respiration  have  disappeared  ?  If  this  were  so,  we  can 
understand  that  the  segmental  ganglia  for  gill-respi- 
ration in  the  medulla  begin  to  be  active  first.  Their 
activity  is  the  stimulus  for  the  activity  of  the  next 
lower  segmental  ganglion,  and  so  on. 

If  we  cut  the  cord  between  medulla  and  phrenic 
nerve,  respiration  must  stop.  But  if  we  could  keep 
such  an  animal  alive  long  enough,  the  lower  segmen- 
tal ganglia  would  be  altered  in  such  a  way  as  to 
breathe  automatically  again. 

That  the  shock-effect  after  such  an  operation  can- 
not be  due  to  an  exhaustion  of  the  phrenic  ganglia  is 
made  obvious  by  the  following  experiment :  W.  T. 
Porter  made  hemisections  of  the  spinal  cord  between 
the  medulla  oblongata  and  the  origin  of  the  phrenic 
nerves  (3).  If  one  half,  for  instance  the  left  half,  of 
the  medulla  be  cut,  the  left  half  of  the  diaphragm  no 
longer  partakes  in  the  respiratory  movements,  while 
the  respiratory  motions  of  the  right  half  continue. 
But  if  the  right  phrenic  be  cut,  the  left  half  of  the 
diaphragm  begins  its  rhythmical  motion  again,  while 
the  right  half  of  the  diaphragm  stops  breathing.  It 
is  of  course,  at  present,  just  as  impossible  to  explain 
why  the  cutting  of  the  right  phrenic  nerve  causes  the 
left  half  of  the  diaphragm  to  breathe  again,  as  it  is  to 
explain  why  a  frog  that  had  lost  its  spontaneity  after 


EXPERIMENTS  ON  AR  THRO  PODS  1 1 3 

an  operation  In  the  thalamus  opticus  begins  to  move 
spontaneously  again  if  the  optic  lobes  and  the  pars 
commissuralis  of  the  medulla  are  removed. 

In  Limulus  an  anterior  and  a  posterior  nerve 
originate  from  every  ganglion  of  the  ventral  chain. 
It  was  interesting  to  determine  whether  these  nerves 
have  functional  differences  like  those  of  the  anterior 
and  posterior  roots  of  the  spinal  cord  of  Vertebrates. 
It  has  been  maintained  that  Arthropods  are  Verte- 
brates that  walk  on  their  backs.  Faivre  has  stated 
that  there  is  not  only  a  separation  of  the  motor  and 
sensory  roots  in  Arthropods,  corresponding  to  Bell's 
law,  but  that  also  in  Arthropods,  in  contrast  with  Ver- 
tebrates, the  ventral  side  of  the  ganglia  is  sensory,  the 
dorsal  motor.  Now  this  Is  not  true  of  the  nerve- 
roots  which  start  from  the  ganglia  in  Limulus.  If  the 
posterior  nerve  be  severed  and  Its  peripheral  stump 
stimulated,  we  get  Inspiratory  movements  of  the  half 
of  the  gills  to  which  this  nerve  goes.  All  the  other 
gills  are  unaffected.  Hence  this  nerve  contains 
motor  fibres.  If  the  ventral  stump  be  stimulated, 
the  whole  animal  becomes  much  excited.  From  this 
we  see  that  the  posterior  nerve  also  contains  sensory 
fibres.  If  the  anterior  nerve  be  severed,  stimulation 
of  the  peripheral  stump  has  no  effect.  Stimulation 
of  the  central  stump  excites  the  entire  animal.  Hence 
the  anterior  nerve  is  purely  sensory.  Limulus  Is 
better  adapted  for  deciding  this  question  than  the 
smaller  Arthropods.  The  conditions  in  the  latter  are 
probably  the  same  as  in  the  former,  for  Vulplan  (4) 


114    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

and  latterly  Bethe  (5)  energetically  reject  the  Idea 
that  dorso-ventrally  the  gangllon-chain  of  Arthropods 
is  the  reverse  of  the  spinal  cord  of  Vertebrates. 

4.  We  will  now  turn  our  attention  to  the  crayfish 
as  the  next  representative  of  the  Arthropods  whose 
braln-physlology  has  been  carefully  Investigated.  Fig. 
32  gives  a  diagram  of  the  central  nervous  system  of 
the  lobster,  which  Is  almost  Identical  with  that  of  the 
crayfish,  o  Is  the  supracesophageal  ganglion  with 
the  nerves  for  the  eyes  and  antennae.  In  addition  It 
gives  off  the  sympathetic  nervous  system  which  goes  to 
the  Intestine.  Both  oesophageal  commissures,  c,  go 
backwards  to  the  subcesophageal  ganglion,  u.  The 
latter  is  seemingly  one  ganglion,  but  it  supplies  six 
pairs  of  segmental  organs,  namely,  the  mouth-ap- 
pendages. The  microscopical  examination  shows  that 
this  subcesophageal  ganglion  In  reality  consists  of  six 
separate  ganglia.  We  often  meet  with  a  fusion  of 
ganglia,  and  consequently  an  apparent  lack  of  clear- 
ness In  the  segmental  arrangement.  It  is  due  to  this 
fact  that  in  the  brain-physiology  of  Vertebrates  the 
segmental  arrangement  of  the  central  nervous  system 
has  been  left  entirely  out  of  consideration.  Next 
after  the  subcesophageal  ganglion  come  the  five 
thoracic  ganglia  (I-V  T,  Fig.  32)  belonging  to  the 
segments  of  the  forceps  and  the  four  pairs  of  loco- 
motor appendages.  In  addition  to  these,  there  are 
the  five  ganglia  of  the  abdomen  (I-V  Abd,,  Fig.  32) 
that  Innervate  the  swimmerets,  and  the  tail,  which 
serves  as  a  swimming-organ.     The  best  experiments 


Fig.  32.    Lobster  with  Central  Nervous  System 
Exposed. 

.,supra«sophageal  ganglion  (brain);  ..commissure;  «,  ^f  oesophageal 
ganglion;  /-Fr,  five  thoracic  ganglia  ; /-K^  3^.,  first  five  abdominal 

ganglia. 

"5 


ii6    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

on  the  central  nervous  system  of  these  animals  have 
unquestionably  been  made  by  Bethe,  and  we  shall  in 
the  main  follow  his  presentation.  Many  of  the  facts 
which  Bethe  describes  from  the  animals  used  in  his 
experiments  are  familiar  to  me  from  personal  observ- 
ation, and  I  am  convinced  that  the  picture  he  gives 
is  correct. 

If  in  a  crayfish  both  the  commissures  {c.  Fig.  32) 
which  connect  the  supraoesophageal  ganglion  0  with 
the  rest  of  the  brain  be  severed,  the  behaviour  of  the 
animal  is  no  longer  controlled  by  the  brain  0,  It  does 
not  make  spontaneous  progressive  movements.  When 
stimulated  it  begins  to  move,  but  after  having  gone 
about  20  cm.  it  stops.  This  lack  of  spontaneous  pro- 
gressive movements  agrees  with  the  description  given 
by  Flourens  of  the  Vertebrate  from  which  the  cere- 
bral hemispheres  had  been  removed.  Flourens's  repre- 
sentation was  wrong,  however,  for  a  dog  operated 
upon  in  this  way  shows  increased  spontaneity  in  its 
progressive  movements. 

Annelids  and  Arthropods  are  closely  related  as  re- 
gards the  central  nervous  system.  However,  Nereis 
shows  an  excess  of  progressive  movements  after 
removal  of  the  supraoesophageal  ganglion,  while  As- 
tacus  no  longer  moves  spontaneously.  I  believe  that 
the  difference  depends  only  upon  circumstances  of 
minor  importance.  Ward  has  already  found — and 
Bethe  has  confirmed  the  fact — that  in  brainless  cray- 
fish the  legs  are  unceasingly  active,  either  cleaning 
each    other    or    performing   pendulum -movements. 


EXPERIMENTS  ON  AR  THRO  FOBS  1 1 7 

They,  however,  make  no  progressive  movements.  I 
beheve  this  is  due  possibly  to  a  secondary  effect  of 
the  extirpation  of  the  supraoesophageal  ganglion. 
The  legs  of  such  an  animal  have  an  abnormal  posi- 
tion, being  more  strongly  flexed  at  the  joints  nearest 
the  body  than  they  are  normally.  The  tension  of 
the  extensors  probably  suffered  severely  from  the 
operation.  Such  mechanical  disturbances  might  easily 
cause  difficulty  in  locomotion,  while  simple  pendulum- 
movements  of  the  legs,  which  require  practically  no 
labor,  could  still  be  performed.  The  fact  that  after  re- 
moval of  the  brain  of  crayfish  the  tension  of  the  flex- 
ors predominates  in  certain  joints  is  of  interest,  as  we 
meet  with  the  same  phenomenon  in  dogs  that  have 
lost  the  anterior  region  of  the  cerebral  hemispheres, 
and  as  it  also  comes  to  our  attention  in  man  after 
apoplexies  which  result  in  the  paralysis  of  an  arm. 

Bethe  concludes  from  these  pendulum-movements 
that  the  brain  is  an  organ  of  inhibition.  As  regards 
this,  the  remarks  hold  good  that  have  already  been 
made  in  this  connection  on  annelids  (see  p.  94). 

The  weakening  of  the  muscles  in  the  crayfish  whose 
brain  has  been  extirpated  shows  itself  also  in  the  fact 
that  the  forceps  no  longer  pinch  as  hard  as  those  of 
normal  animals. 

After  what  has  been  said  concerning  the  segmental 
character  of  the  central  nervous  system,  it  is  to  be 
expected  in  the  crayfish  that,  since  the  segmental 
ganglia  of  the  organs  of  mastication  are  located  in 
the  suboesophageal  ganglion,  extirpation  of  the  supra- 


ii8    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

oesophageal  ganglion  will  not  interfere  with  the  nor- 
mal character  of  its  eating  movements.  I  give  the 
description  in  Bethe's  words  :  **  The  animal  devoid  of 
the  supraoesophageal  ganglion  is  able  to  eat  and 
selects  its  food.  It  is  true  that  pebbles,  small 
pieces  of  wood,  etc.,  are  seized  by  the  forceps  of  the 
front  pairs  of  legs,  but  when  brought  near  the  mouth 
they  are  rejected.  A  piece  of  meat,  however,  is 
always  taken  into  the  mouth  and  masticated.  The 
swallowing  is  difficult,  just  as  in  the  case  of  Carcinus. 
The  piece  often  remains  for  a  long  time  between  the 
maxillipedes  without  being  swallowed,  and  at  last  falls 
to  the  ground.  Pieces  of  paper  that  have  been  satu- 
rated with  meat-juice  are  treated  in  the  same  way. 
Stones  that  have  been  covered  with  meat-juice  are 
also  brought  to  the  mouth,  but  no  attempt  is  made  to 
masticate  them.  They  are  usually  dropped  as  soon 
as  they  come  in  contact  with  the  maxillipedes."  Thus 
we  see  that  the  nature  of  the  stimulus  determines  the 
results  just  as  in  the  case  of  Actinians.  The  brain  of 
the  crayfish  has  nothing  to  do  with  these  reactions. 
The  central  nervous  system  is  in  this  case  to  be  con- 
sidered only  as  an  organ  for  the  conduction  of  stimuli, 
a  function  that  could  just  as  well  be  performed  by  plant 
protoplasm  or  muscle-tissue  as  by  nerve-protoplasm. 
In  the  crayfish,  the  original  segmental  arrangement 
of  the  nervous  elements  is  so  well  preserved  that  re- 
moval of  the  brain  does  not  interrupt  the  proto- 
plasmic nervous  connection  between  the  surface  of  the 
mouth  and  the  muscles  of  the  thoracic  appendages. 


EXPERIMENTS  ON  AR  THRO  PODS  1 1 9 

When  these  animals  from  which  the  brain  has  been 
removed  are  laid  on  their  backs  they  return  to  the 
ventral  position. 

The  observations  made  by  Bethe  In  crayfish  in 
which  he  had  severed  the  oesophageal  commissures 
on  only  one  side  are  interesting.  The  division  was 
made  on  the  right  side.  If  he  touched  the  left  side  of 
the  head  of  such  an  animal,  first  the  forceps  of  the 
stimulated  side  reached  toward  the  stimulated  spot 
and  then  those  of  the  other  side  followed  with  accur- 
acy. At  the  same  time,  the  animal  attempted  to  escape 
backwards.  If  the  same  stimulus  was  applied  to  the 
right  side  of  the  head,  the  forceps  did  not  react.  Even 
with  a  strong  stimulus  no  reaction  followed.  Hence 
the  stimulus  that  produces  the  localising  reflex  can  only 
be  transmitted  through  the  longitudinal  commissure  of 
the  same  side  to  the  appendages.  This  seems  to  hold 
good  generally  for  the  Arthropods,  since  Bethe  was  able 
to  prove  it  in  Carcinus,  Squilla,  and  Hydrophylus.  It 
seems  to  hold  good  not  only  for  the  conduction  through 
the  oesophageal  commissures  but  through  all  longitu- 
dinal commissures.  After  division  of  an  oesophageal 
commissure,  circus-motions  often  but  not  always  occur 
toward  the  normal  side.  The  animal  is  also  able  to 
move  straight  ahead,  but  this  requires  some  effort. 

If  the  right  oesophageal  commissure  be  severed,  the 
tonus  of  the  muscles  on  the  right  side  (the  injured 
side)  of  the  abdomen  is  diminished,  and  as  a  result 
the  abdomen  is  curved  toward  the  left  and  becomes 
concave  on  that  side. 


I20    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

Division  of  the  brain  in  the  middle  Hne — that  is, 
separation  of  the  two  halves  of  the  brain — destroys  the 
geotropic  reactions  of  the  eyestalks.  It  is  still  more 
remarkable  that  such  animals  no  longer  prefer  to  re- 
main in  the  dark  like  normal  animals. 

If  the  longitudinal  commissures  be  divided  between 
the  mouth-ganglia  (subcesophageal  ganglion)  and  the 
ganglion  of  the  chelae,  all  locomotor  movements  be- 
come impossible,  although  the  legs  are  not  paralysed. 
This  is  strange,  because  the  subcesophageal  ganglion 
contains  the  segmental  nerve-elements  of  the  oral  ap- 
pendages but  not  those  of  the  locomotor  appendages. 
In  other  Crustaceans, extirpation  of  the  subcesophageal 
ganglion  has  no  such  paralysing  efifect  on  the  loco- 
motor movements.  It  is  impossible  to  tell  at  present 
what  causes  the  exceptional  behaviour  of  Astacus  in 
this  regard.  I  do  not  believe  we  are  obliged  to  as- 
sume that  this  is  an  instance  of  a  deviation  from  the 
laws  of  the  segmental  arrangement  of  the  nerve-ele- 
ments (centres)  of  the  limbs.  This  is  shown  by  the 
fact  that  the  legs  of  such  an  animal  are  not  paralysed, 
but  are  unceasingly  occupied  in  cleaning  the  abdo- 
men, the  pedes  spurii,  or  each  other.  Indeed,  more 
than  that,  *'  if  we  give  one  of  the  forceps  of  a  loco- 
motor appendage  a  piece  of  meat  or  paper,  other 
legs  approach  immediately,  seize  the  meat,  and  carry 
it  to  the  mouth,"  in  spite  of  the  fact  that  all  nervous 
connection  between  the  nerves  of  the  mouth-organs 
and  the  legs  has  been  severed.  It  is  true  that  the  ap- 
pendages around  the  mouth  often  refuse  to  accept 


EXPERIMENTS  ON  ARTHROPODS  121 

and  forward  the  pieces  of  meat  that  are  thus  offered 
them  by  the  legs. 

As  regards  the  further  Isolation  of  the  ganglia  that 
are  located  posterior  to  the  suboesophageal  ganglion, 
the  facts  which  have  been  described  in  LImulus  are 
in  general  true.  As  long  as  the  ganglion  of  a  seg- 
ment remains  connected  with  the  segmental  organs, 
the  functions  of  that  segment  remain  unimpaired. 
Bethe  has  found  single  exceptions  to  this  rule,  but  it 
is  conceivable  that  these  exceptions  are  shock-effects 
resulting  from  the  operation. 

We  will  now  report  more  briefly  concerning  Bethe's 
experiments  on  some  other  Arthropods. 

5.  Squilla  no  longer  swims  spontaneously  after  the 
supraoesophageal  ganglion  has  been  isolated  (that  is, 
after  division  of  the  commissure  between  the  supraoe- 
sophageal ganglion  and  the  mouth-ganglion).  The 
spontaneous  progressive  movements  usually  seem  to 
be  destroyed.  When  stimulated,  however,  the  ani- 
mal moves  normally.  The  nervous  mechanism  for 
the  locomotor  reflexes  is  localised  in  the  three  ganglia 
of  the  locomotor  appendages,  that  is,  these  append- 
ages still  move  normally,  even  though  the  connection 
with  the  ganglia  lying  in  front  has  been  interrupted. 

In  grasshoppers  (JPachytylus  cinerascens)  isolation 
of  the  supraoesophageal  ganglion  causes  the  spontan- 
eous progressive  movements  to  cease.  These  animals, 
after  the  operation,  clean  their  antennae  with  their 
fore-legs  like  a  normal  animal.  According  to  Bethe 
these  localised  reflexes  of  the  legs  are  produced  by 


122    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

the  stimulus  of  the  operation.  Abnormal  positions 
of  the  legs,  resulting  from  the  operation,  occur  just  as 
in  Astacus  and  Squilla. 

If  the  supra-  and  subcesophageal  ganglia  be  re- 
moved by  decapitating  the  animals,  they  are  still  able 
to  perform  some  walking  movements,  and  especially 
hopping  movements,  when  stimulated.  This  agrees 
with  the  idea  of  the  preservation  of  the  purely  seg- 
mental arrangement  of  the  nerve-connections.  Yer- 
sin  s  experiments  on  crickets  are  very  significant  in 
this  regard.  I  take  them  from  Bethe's  paper.  They 
deal  with  crickets  from  which  both  longitudinal  com- 
missures had  been  removed  between  the  subcesophag- 
eal ganglion  and  the  first  thoracic  ganglion.  Yersin 
kept  these  animals  alive  for  weeks.  "■  When  laid  on 
their  backs  they  were  able  to  turn  over.  When  stim- 
ulated they  moved  forward  a  few  steps,  or  to  the  side, 
according  to  the  point  of  stimulation.  In  doing  so 
they  occasionally  tumbled  over.  When  stimulated, 
they  still  made  attempts  at  flying  without  being  able 
to  lift  themselves  from  the  ground."  Yersin  observed 
that  a  male  and  a  female,  both  of  which  had  been  op- 
erated upon  in  this  way,  were  able  to  pair.  Of  course 
it  was  necessary  to  place  the  male  on  the  female  in 
this  case.  The  male  on  which  he  made  this  observ- 
ation had  already  given  off  a  spermatophore. 

Bees  lived  only  a  short  time  after  the  extirpation 
of  the  supracesophageal  ganglion.  The  bee  shows 
the  same  restlessness  that  was  noticed  in  Astacus. 

Bees   whose   brains   were    divided   lengthwise    in 


EXPERIMENTS  ON  ARTHROPODS  123 

symmetrical  halves  showed  a  perceptible  functional 
disorder  only  in  their  behaviour  toward  the  hive.  *'  If 
carried  back  to  it  they  crawl  about  on  the  board  be- 
fore the  entrance  but  make  no  attempt  to  enter,  and 
they  pay  no  attention  to  their  companions." 

If  bees  be  decapitated,  the  supra-  and  suboesopha- 
geal  ganglion  being  thus  removed,  they  are  still  able 
to  walk,  although  awkwardly.  When  laid  on  their 
backs  they  turn  over  with  the  help  of  their  legs. 
"  When  stimulated  on  the  ventral  side  they  grasp  the 
object  (pencil)  with  their  legs,  pull  it  toward  them, 
bend  the  abdomen,  and  attempt  to  sting  it."  But  not 
all  anirnals  give  such  favourable  results.  In  brain- 
physiology  only  those  animals  operated  upon  which 
show  the  slightest  disorders  can  be  considered,  be- 
cause the  exhaustion  may  render  the  rest  of  the  cen- 
tral nervous  system  pathological. 

As  was  to  be  expected  a  priori  on  the  basis  of  the 
segmental  theory,  the  stinging-reflex  is  possible  as  long 
as  the  abdominal  ganglion  is  preserved.  Bethe  showed 
that  the  abdomen,  when  severed  from  the  body,  still 
bends  if  stimulated  on  the  ventral  side  and  reaches 
the  stimulated  spot  with  the  outstretched  sting.  At 
the  same  time  poison  is  ejected.  The  reflex  also 
continues  when  all  the  abdominal  segments  with  the 
exception  of  the  last  one  have  been  amputated. 

If  the  supraoesophageal  ganglion  in  a  water-beetle 
(Hydrophilus)  be  extirpated,  the  progressive  loco- 
motor  movements  are  not  only  not  interrupted,  but  the 
animal  goes  about  almost  unceasingly,   showing  only 


124    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

modifications  which  suggest  that  the  relation  in  the  ten- 
sion of  the  antagonistic  muscles  of  its  legs  is  changed. 
The  animal  turns  out  for  obstacles  that  come  in  its 
way.  If  a  beetle  that  has  lost  the  supracesophageal 
ganglion  is  thrown  into  water  it  swims  off,  drawing  in 
the  first  pair  of  legs.  The  normal  water-beetle  rests 
quietly  under  dark  objects.  The  water-beetle  whose 
supracesophageal  ganglion  has  been  divided  by  a 
longitudinal  incision  no  longer  shows  these  reactions, 
although  the  light  is  still  able  to  produce  other  effects 
in  the  animal.  If  suddenly  exposed  to  strong  light 
or  a  dark  shadow — when  in  motion,  namely — it  ceases 
to  move. 

An  animal  whose  right  oesophageal  commissure  has 
been  severed  does  not  brace  itself  against  obstacles  as 
strongly  with  the  legs  of  the  right  side  as  with  those 
of  the  left  side.  It  seems  to  me  this  shows  that  the 
extensors  of  the  right  side  are  weakened,  as  it  is  they 
that  have  to  perform  the  task  of  bracing.  Further- 
more, the  right  legs  are  moved  constantly.  It  may 
be  possible  that  these  two  facts  are  in  some  way  con- 
nected. The  decreased  opposition  of  the  extensors 
renders  the  pendulum-movements  of  the  legs  easier. 
The  same  explanation  may  hold  for  Astacus,  bees,  etc. 
If  the  supra- and  suboesophageal  ganglia  be  extirpated, 
the  animal  only  makes  progressive  movements  when 
stimulated.  But  the  ability  to  perform  coordinated 
progressive  movements  is  not  destroyed.  When  laid 
on  its  back  the  animal  still  tries  to  regain  the  ventral 
position,  but  the  efforts  made  by  the  legs  are  vain. 


EXPERIMENTS  ON  ARTHROPODS 


125 


If  put  under  water  it  still  makes  swimming  move- 
ments, but  these  do  not  help  it  forward. 

The  experiments  on  the  other  ganglia  of  this  ani- 
mal performed  by  Bethe  do  not  concern  us  in  this 
book.  We  will  only  quote  that  result  of  Bethe's 
which  is  of  most  importance  for  our  purpose  :  '*  Nei- 
ther the  suboesophageal  nor  the  prothoracic  ganglion 
is  the  seat  of  the  reflex  for  righting  the  animal  when 
turned  on  its  back,  nor  of  the  coordination  of  the  mus- 
cles of  locomotion,  walking,  or  swimming,  as  Faivre 
maintains.  It  would  seem  as  though  these  reflexes 
were  located  rather  in  each  thoracic  gayiglion  for  the  cor- 
responding segment  T  This  last  sentence  expresses  the 
principal  truth  for  all  complicated  central  nervous  sys- 
tems. Each  segment  of  a  segmented  animal  may  be 
regarded  as  a  simple  reflex  animal,  comparable  to  the 
Ascidian,  and  the  analysis  of  the  reflexes  depends 
upon  the  same  principles  and  leads  to  the  same  re- 
sults in  both  cases.  The  complication  that  appears 
in  segmented  animals  consists  in  the  fact  that  when  a 
process  of  stimulation  takes  place  in  one  segment  it 
is  communicated  to  the  neighbouring  ganglia,  and 
these  ganglia  produce  processes  of  the  same  kind.  It 
is  possible  that  the  nature  of  the  stimulation  also 
helps  to  determine  the  nature  of  the  movement.  The 
assumption  of  special  centres  of  coordination  is 
superfluous.  One  other  fact  is  of  importance  in  exper- 
iments in  extirpating  and  severing  nervous  connec- 
tions, namely,  that  the  division  may  bring  about  in 
those  parts  which  are  protoplasmically  connected  with 


126    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

the  place  of  operation  a  change  which  is  sometimes 
transitory,  sometimes  permanent — the  so-called  shock- 
effects.  The  highest  degree  of  these  shock-effects  is 
attained  in  case  of  degeneration.  It  is  a  remarkable 
fact  that,  in  an  operation  on  the  central  nervous  sys- 
tem, the  effect  of  the  shock  is  much  greater  in  the 
part  posterior  to  the  place  of  operation  than  in  the 
anterior  part,  toward  the  head.  This  may  indicate 
that  there  is  a  constant  current  of  impulses  or  influ- 
ences in  the  direction  from  the  brain  to  the  posterior 
parts  of  the  central  nervous  system.  The  interrup- 
tion of  these  influences  may  be  responsible  for  the 
condition  which  we  call  shock-effects  and  which  may 
be  transitory.  These  shock-effects  are  incomparably 
less  strong  in  cold-blooded  than  in  warm-blooded  ani- 
mals. We  do  not  possess  enough  facts  to  enable  us 
to  give  an  explanation  of  the  shock-effects. 

Bibliography. 

1.  Hyde,  Ida  H.  The  Nervous  Mechanism  of  the  Respiratory 
Movements  of  Limulus  Polyphemus,  journal  of  Morphology^  vol. 
ix.,  1894. 

2.  Langendorff,  O.  Studien  iiber  die  Innervation  der  Athembe- 
wegungen.     I.     Mittheilung.     Archiv  f.  Physiologie,  1880. 

3.  Porter,  W.  T.  The  Path  of  the  Respiratory  Impulse  from 
the  Bulb  to  the  Phrenic  Nuclei,  journal  of  Physiology,  vol.  xvii., 
1894-95. 

4.  VuLPiAN.  Lefons  sur  la  Physiologic  ginirale  et  comparee  du 
Systlme  JSferveux.     Paris,  1866. 

5.  Bethe,  A.  Vergleichende  Ui^tersuchungen  ilber  die  Eunctionen 
des  Centralnervensystems  der  Arthropoden.  Pfliiger's  Archiv^  Bd. 
Ixviii.,  1897. 


EXPERIMENTS  ON  ARTHROPODS  127 

6.  Bethe,  a.  Das  Centralnervensystem  von  Carcinus  mcenas. 
Archiv  f.  microskop.  Anatomie  und  Entwicklungsgeschichte^  Bd.  1., 
1897  ;  Bd.  li.,  1898. 

7.  Steiner,  J.  Die  Functionen  des  Centralnervensystems  und 
ihre  Phylogenese.  III.  Abtheilung.  Die  wirbellosen  Thiere. 
Braunschweig,  1898. 


I 


CHAPTER  VIII 


EXPERIMENTS  ON  MOLLUSKS 


The  literature  on  the  functions  of  the  central 
nervous  system  of  Mollusks  is  extremely  meagre. 
It  is  nevertheless  valuable,  as  it  furnishes  us  with 
further  proofs  of  the  theory  that  the  simple  and 
rhythmical  spontaneity,  as  well  as  reflex  processes,  do 
not  depend  upon  the  brain  or  specific  peculiarities  of 
the  ganglia.      A  Gastropod  whose  brain  (^,  Fig.  33) 

has  been  removed 
continues  to  move 
spontaneously.  Stei- 
ner  has  observed 
this  in  a  transparent 
pelagic  species  of 
snail,  Pterotrachea, 
that  is  about  10  cm. 
long  (i).  The  foot 
of  this  snail  has  been 
transformed  into  a 
swimming  organ.  Neither  one-  nor  two-sided  de- 
struction of  the  supraoesophageal  ganglion  has  the 
slightest    influence     upon    the     character    and    the 

128 


Fig.  33.  Schematic  Representation  of 
THE  Central  Nervous  System  of  a 
Snail  (Paludina  Vivipara). 

J",  brain ;  /',  pedal  ganglion.      (Modified  after  Leydig.) 


EXPERIMENTS  ON  MOLLUSKS 


129 


quantity  of  the  spontaneous  progressive  movements. 
Destruction  of  the  pedal  gangUon,  on  the  other  hand, 
puts  an  end  to  all  locomotion.  Steiner  concludes, 
therefore,  that  "the 
pedal  ganglion  alone 
has  control  of  the  entire 
locomotion  of  the  ani- 
mal." This  anthropo- 
morphic conclusion 
goes  too  far.  The  only 
conclusion  we  are  justi- 
fied in  drawing  from 
this  observation  is,  that 
the  protoplasmic  con- 
necting fibres  between 
the  skin  and  the  foot- 
muscle  of  the  animal 
pass  through  the  gan- 
glion. Steiner  further  attempted  to  see  if  he  could 
produce  circus-motions  by  means  of  a  one-sided  divi- 
sion of  the  oesophageal  commissure  in  other  Mollusks, 
Pleurobranchia  and  Aplysia.  He  succeeded  no  better 
than  in  Pterotrachea.  One-sided  destruction  of  the 
pedal  ganglion  in  Cymbulia,  however,  caused  paralysis 
of  one-half  of  the  locomotor  organ.  The  animal 
naturally  moved  in  a  circle,  for  only  one  wing  served 
as  an  oar. 

The  Cephalopods  have  an  extremely  complicated 
brain  (Fig.  34).  It  consists  of  a  dorsal  and  a  ventral 
mass,  each  of  which  is  composed  of  several  ganglia. 


Fig.  34.     Brain  of  Sepia. 

Cg^  cerebral  ganglion ;  Spg^  supraoesophageal 
ganglion  ;  Bg^  buccal  ganglion  ;  Tg^  ganglia 
of  the  tentacles.    (After  Glaus.) 


I30    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

The  dorsal  and  ventral  ganglia  are  connected  by 
commissures.  In  addition,  they  possess  a  series  of 
peripheral  ganglia,  the  tentacle-ganglia  {Tg,  Fig.  34), 
for  instance.  It  is  of  significance  for  the  segmental 
theory  that  the  tentacle-ganglia  suffice  to  produce  ten- 
tacle-reflexes, as  V.  Uexkull  has  shown  In  Eledone  (2). 
It  has  been  inferred  from  experiments  on  Vertebrates 
that  peripheral  ganglia  cannot  transmit  reflexes. 

Now,  as  regards  experiments  on  the  brain  of  Ceph- 
alopods,  Steiner  reports  as  follows  concerning  Oc- 
topus vulgaris:  ''If  the  dorsal  ganglion  on  one 
side  be  removed,  or  both  commissures  of  one  side  be 
severed,  not  the  slightest  change  is  visible  in  the  life- 
processes  of  the  animal,  for  It  moves  spontaneously  as 
before,  attacks  Its  prey  {Carcinus  mcenas^  cleverly, 
and  devours  It.  But  the  picture  changes  if  the  dorsal 
ganglion  be  entirely  removed.  To  be  sure  the  two 
forms  of  locomotion  are  preserved,  for  the  animal 
creeps  with  the  aid  of  its  arms,  or  shoots  like  an  arrow 
through  the  waves,  when  water  is  forced  out  of  the 
mantle-cavity  rhythmically.  These  movements  are, 
however,  no  longer  spontaneous^  for  they  occur  only 
when  the  animal  Is  stimulated,  neither  does  it  take 
Its  food  spontaneously.  The  normal  octopus,  which 
is  endowed  with  marked  intelligence  [  ?  ],  is  wont  to 
observe  its  surroundings  most  attentively,  but  now  It 
sits  indifferent  to  Its  surroundings,  as  though  idiotic, 
and  only  its  regular  breathing  gives  evidence  that  it 
still  lives.  Vision  Is  unimpaired,  for  it  draws  back 
when  a  stick  Is  brought  toward  its  eye."     V.  Uexkull's 


EXPERIMENTS  ON  MOLLUSKS  131 

article  on  Eledone  is  more  exhaustive  than  Steiner  s. 
One  of  his  observations,  describing  the  extraordinarily 
excited  condition  of  an  animal  whose  cerebral  gan- 
glion had  been  removed,  is  worthy  of  mention.  "  All 
the  reflexes  seemed  increased.  When  anyone  ap- 
proached the  basin  the  Eledone  that  had  undergone 
this  operation  swam  off,  while  the  normal  animals 
remained  quiet.  There  was  an  incessant  play  of 
colors.  During  the  second  night,  in  spite  of  the  pro- 
tecting net,  it  escaped  and  died  on  the  floor  of  the 
laboratory."  V.  Uexkull  concludes  from  this  that  there 
are  inhibitory  centres  in  the  cerebral  ganglion.  We 
have  seen  that  Bethe  arrived  at  a  similar  conclusion 
in  regard  to  the  supraoesophageal  ganglion  of  the 
Arthropods.  We  have  discussed  this  possibility  in 
connection  with  Maxwell's  experiments  on  Nereis. 

The  arm-nerves  originate  in  the  pedal  ganglion. 
But  the  latter  is  connected  with  the  supraoesophageal 
ganglion  directly  by  means  of  the  anterior  commis- 
sures and  indirectly  by  means  of  the  posterior  commis- 
sures. Now  it  is  of  interest  to  know  that  the  influence 
which  the  anterior  part  of  the  supraoesophageal  gan- 
glion exerts  on  the  arm-movements  when  stimulated 
is  exactly  the  opposite  of  that  exerted  by  the  posterior 
part ;  if  the  entire  supraoesophageal  mass  between 
both  pairs  of  commissures  be  separated  by  a  frontal 
incision  and  both  stumps  be  stimulated  down  deep, 
where  the  central  ganglia  are  located,  according  to  v. 
Uexkull,  we  obtain  the  following  results  :  Stimulation 
of  the  anterior  stump  causes  the  cup-like  suckers  to 


132    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

take  hold  strongly  ;  stimulation  of  the  posterior  stump 
causes  the  suckers  to  let  go  and  the  arms  to  be  with- 
drawn. Thus  the  antagonistic  activities  of  the  arms 
depend  upon  two  different  parts  of  the  central  nervous 
system.  "  An  animal  whose  supra  oesophageal  mass 
has  been  divided  in  the  vicinity  of  the  first  central 
ganglion  behaves  like  an  animal  that  is  only  able  to 
take  hold  of  objects.  It  grasps  every  object  firmly 
and  liberates  itself  again  only  with  difficulty.  It 
usually  retains  its  hold  and  sits  with  extended  arms, 
or  crawls  forward  with  the  greatest  difficulty.  Such 
an  animal  placed  on  the  back  of  a  torpedo  seizes  it 
firmly  with  the  arms,  and  no  shocks  of  the  electric 
organs  are  of  avail  to  rid  the  fish  of  its  burdensome 
rider.  On  the  other  hand,  it  is  evident  that  the  Ele- 
done  only  participates  in  the  ride  involuntarily  from 
the  fact  that  it  becomes  dark  brown  and  throws  ink. 
If  a  normal  Octopus  by  mistake  grasps  after  a  tor- 
pedo, it  never  remains  in  so  dangerous  a  neighbor- 
hood more  than  a  few  seconds  [I  have  observed 
this  in  Octopus,  never  in  Eledone]."  It  seems  to  me 
that  the  conclusion  to  be  drawn  from  these  facts  is, 
that  the  anterior  and  posterior  parts  of  the  supra- 
oesophageal  ganglion  are  connected  with  antagonistic 
muscle-groups.  This  relation  is  of  interest  in  view  of 
galvanotropic  experiments,  which  we  shall  discuss 
later  on.  It  is  furthermore  probable  from  v.  Uex- 
kiill's  experiments  that  the  act  of  eating  depends  upon 
the  integrity  of  the  first  central  ganglion,  while  the 
second  and  third  central  ganglia  are  necessary  for  all 


EXPERIMENTS  ON  MOLLUSKS 


133 


the  remaining  functions  of  the  arms,  for  instance,  loco- 
motion and  steering. 

The  fact  discovered  by  v.  Uexkull  that  the  basal 
ganglion,  when  no  longer  connected  with  the  central 
nervous  system,  produces  coordinated  chewing  move- 
ments when  stimulated  is  of  great  importance  for  the 
segmental  theory.  The  skin  and  muscles  are  in  this 
case  connected  by  nerve-fibres  which  do  not  pass 
through  the  central  nervous  system  but  through  a 
peripheral  ganglion  that  v.  Uexkull  terms  the  bucco- 
intestinal  ganglion.  This  is  another  fact  that  speaks 
for  the  idea  that  the  ganglia  are  only  to  be  considered 
as  organs  of  transmission,  that  is,  as  connecting  pro- 
toplasmic threads  for  reflexes,  and  not  as  bearers  of 
mysterious  reflex  mechanisms. 

BIBLIOGRAPHY. 

1.  Steiner,  J.  Die  Eunctionen  des  Centralnervensy stems  der 
wirbellosen  Thiere.  Sitzungsberichte  der  Berliner  Academie  der 
Wissenschaften^  1890?  i-*  P-  32. 

2.  V.  Uexkull.  Physiologische  Untersuchungen  an  Eledone 
moschata.     Zeitsch.  f.  Biologie^  Bd.  xxxi.,  1895. 

3.  Steiner,  J.  Die  Eunctionen  des  Centralnervensy stems  und 
ihre  Phylogenese.  III.  Abtheilung.  Die  wirbellosen  Thierey  Braun- 
schweig, 1898. 


CHAPTER  IX 

THE  SEGMENTAL  THEORY  IN  VERTEBRATES 

I.  The  segmental  arrangement  of  the  central  nerv- 
ous system  of  Vertebrates  is  suggested  by  the  ar- 
rangement of  the  spinal  nerves.  The  number  of 
segmental  ganglia  present  in  the  head  exceeds  the 
number  of  cranial  nerves.  The  auditory  nerve  and 
the  vagus,  for  instance,  originate  from  more  than  one 
segment  each.  Dohrn,  Locy,  and  others  have  shown 
this.  Locy  states  that  there  are  originally  fourteen 
segments  in  the  head  of  the  embryo  of  the  shark, 
while  there  are  only  twelve  cranial  nerves.  Physi- 
ology is  more  interested  in  the  decision  of  this  quest- 
ion than  morphology,  because  upon  it  depends  the 
theory  of  coordinated  movements.  The  question 
of  segmentation  may  also  be  of  importance  indi- 
rectly in  connection  with  the  idea  of  localisation  in 
the  cerebral  hemispheres,  for  the  so-called  centres  of 
the  cerebral  cortex  are  merely  the  places  where  the 
fibres  from  single  segments  of  the  central  nervous 
system  enter. 

The  spinal  nerves  originate  in  the  spinal  cord,  and, 

134 


EXPERIMENTS  ON  VERTEBRATES  135 

as  has  been  said  above,  suggest  externally  its  segmental 
character.  Each  has  a  ventral  motor  and  a  dorsal 
sensory  root,  and  we  desire  to  call  attention  to  the 
fact  that  the  dorsal  root  passes  through  a  ganglion 
(the  spinal  ganglion).  If  the  ventral  root  be  severed, 
paralysis  of  the  muscles  of  the  corresponding  segment 
occurs.  If  the  dorsal  root  be  severed,  the  correspond- 
ing segment  becomes  insensible,  or,  more  properly 
speaking,  the  transmission  of  impulses  which  proceed 
from  the  periphery  to  the  muscles  of  this  segment  and 
to  the  remaining  segments  becomes  impossible.  The 
operation  itself,  however,  has  still  another  influence 
on  the  tension  of  the  muscles  of  the  same  segment 
(perhaps  also  of  other  segments).  The  amount  of  the 
muscle-tension  under  normal  conditions  varies  (prob- 
ably with  the  chemical  conditions  of  the  muscles).  If 
a  muscle  be  stretched  with  a  certain  weight  it  attains  a 
certain  length.  But  if  the  posterior  nerve-roots  be 
severed  while  the  muscle  is  still  nervously  connected 
with  its  segment  the  muscle  lengthens  (E.  v.  Cyon). 
The  operation  causes  a  shock,  in  other  words,  prob- 
ably a  chemical  change  in  the  muscle.  The  nature  of 
this  change  is  as  yet  unknown.  This  influence  of  the 
posterior  roots  on  the  muscles  shows  itself  also  in  the 
movements  of  an  animal  in  which  the  posterior  roots 
of  the  hind-legs  have  been  severed  :  the  movements  of 
the  legs  are  disturbed.  It  is  known  that  the  nerves 
of  the  brain  are  also  of  segmental  origin,  only  in  this 
case  the  inequalities  of  growth  obliterate  externally 
the  segmental  relations.    From  the  fact  that  the  chiefly 


136    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

sensory  trigeminus,  which  may  be  considered  as  the 
posterior  root  of  the  faciaHs,  possesses  a  peripheral 
gangHon  (gangHon  Gasseri),  while  the  chiefly  motor 
facialis  has  no  peripheral  ganglion,  Bell  concluded 
that  the  posterior  roots  of  the  spinal  cord,  which  pos- 
sess peripheral  ganglia,  are  sensory,  while  the  anterior 
roots,  which  possess  no  ganglia,  are  motor.  Bell 
found  (by  means  of  vivisection)  that  division  of  the 
trigeminus  produces  disturbances  in  eating  in  those 
animals  that  take  their  food  with  the  lips :  these 
disturbances  are  caused,  naturally,  by  the  weakness  of 
the  corresponding  muscles. 

We  will  add  a  word  here  concerning  the  import- 
ance of  the  ganglion-cells  for  the  preservation  of  the 
axis  cylinder.  The  axis  cylinder  may  be  regarded  as 
a  protoplasmic  extension  of  a  ganglion-cell,  which 
lives  only  as  long  as  it  is  connected  with  the  cell. 
Now  the  ganglion-cells  of  the  dorsal  roots  are  located 
in  the  spinal  ganglion,  those  of  the  ventral  roots  in 
the  ventral  horns  of  the  spinal  cord.  If  the  posterior 
roots  be  severed,  that  part  of  the  fibres  which  is  con- 
nected with  the  spinal  cord  degenerates,  while  the 
part  that  is  connected  with  the  spinal  ganglion  is 
preserved,  and  grows  or  regenerates.  If  the  ventral 
roots  be  severed  the  peripheral  stump  degenerates, 
while  the  stump  that  is  still  connected  with  the  spinal 
cord  is  preserved  and  grows.  We  may  mention  here 
briefly  that  the  nerve-fibres  of  the  posterior  roots, 
according  to  Golgi's  school,  are  not  fused  with  the 
ganglion-cells  of  the   posterior  horns   in    the    spinal 


EXPERIMENTS  ON  VERTEBRATES  137 

cord,  but  are  only  in  contact  with  them/  For  the 
transmission  of  the  impulse  this  fact  is  of  no  import- 
ance ;  it  is  not  necessary  in  either  case  that  the  gan- 
glion-cells of  the  posterior  horn  and  the  sensory 
nerves  be  grown  together,  they  need  only  to  be  in 
sufficiently  close  contact.  Engelmann  called  atten- 
tion to  these  relations  long  ago  in  his  excellent  article 
on  conduction  in  the  ureter. 

2.  Sufficient  data  exist  for  proving  the  segmental 
localisation  of  reflexes  in  the  spinal  cord.  In  a  dog 
whose  spinal  cord  has  been  severed  somewhere  in  the 
thoracic  region  the  posterior  part  is  entirely  separated 
from  the  anterior  part  as  far  as  the  motor  and  sensory 
functions  are  concerned.  Immediately  after  the  oper- 
ation severe  shock-effects  appear,  but  these  are  only 
temporary,  and  we  shall  return  to  this  subject  later. 
The  interruption  of  the  continuity  is  permanent,  for 
in  the  central  nervous  system  of  higher  animals  no  re- 
generation has  been  observed,  but  only  a  healing 
together  of  the  cut  surfaces  by  means  of  connective 
tissue.  In  such  an  animal  the  part  located  behind  the 
point  of  division  shows  all  the  reactions  which  are 
possible  in  the  corresponding  segments.  Goltz  has 
proved  this  for  dogs.  Rubbing  of  the  skin  produces 
scratching  movements  of  the  hind-legs  ;  erection  of 
the  penis  and  urination  can  be  produced  by  stimulat- 
ing the  foreskin.  The  reflexes  of  the  rectum  and 
bladder  and  the  vasomotor  reactions  are  intact.    We 

'  Apathy's  publications  arouse  suspicion  as  regards  the  results  obtained  by 
Golgi's  methods. 


138    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

have  already  called  attention  to  the  fact  that  the  re- 
spiratory movements  are  segmental  processes.  Goltz 
has  shown  that  those  reflexes  in  which  the  muscles  of 
the  arms  are  active  are  also  segmental  (2).  During 
the  period  of  heat  the  male  frog  clasps  the  female 
with  his  fore-limbs.  If  the  head  and  back  part  of  the 
body  of  a  male  frog  be  amputated  during  this  time, 
so  that  only  a  piece  consisting  of  the  arms  and  the 
segmental  piece  of  the  spinal  cord  belonging  with  the 
arms  remains,  rubbing  the  skin  on  the  ventral  side  of 
this  piece  suffices  to  produce  the  clasping  reflex. 

3.  In  considering  the  brain  of  Vertebrates  we  are 
obliged  to  deal  with  the  brain  of  the  cold-blooded 
animals,  for  the  simple  reason  that  in  warm-blooded 
animals  we  cannot  well  perform  brain-operations  in 
the  vicinity  of  the  medulla  oblongata  without  having 
the  respiration  cease.  In  cold-blooded  animals  the 
shock-effects  are  not  so  great.  We  have  selected  the 
brain  of  the  frog  as  a  type  because  it  has  been  worked 
out  the  most  carefully.  It  consists  chiefly  of  the 
cerebral  hemispheres  {GH,  Fig.  35),  thalamus  op- 
ticus {Th.,  O),  optic  lobe,  cerebellum  {KH),  and 
medulla  oblongata.  The  diagram  (Fig.  35)  gives  the 
origin  of  the  nerves  of  the  brain  (V-XI).  It  is  our 
aim  to  show  in  this  chapter  that  the  individual  activi- 
ties of  the  frog  are  dependent  upon  the  segmental 
ganglia  and  that  we  have  no  right  to  speak  of  **  cen- 
tres" for  the  single  activities  unless  the  word  centre  Is 
synonymous  with  the  expression  segmental  ganglion. 

We  will  first  consider  the  coordinated  progressive 


EXPERIMENTS  ON  VERTEBRATES 


139 


movements.     It  was  for  a  long  time  a  dogma  that 
progressive  locomotive  movements  could  only  be  per- 
formed by  frogs  that  were  still  in  possession  of  their 
cerebral    hemispheres. 
This     statement     was 
made  by  Flourens.  He 
observed     that     frogs 
devoid  of  the  cerebral 
hemispheres  no  longer 
move      spontaneously 
(3).      Later  on  Schra- 
der  showed   that   this 
observation    was    not 
correct ;  that  this  lack 
of     spontaneity     only 
occurs  when  the  thai- 
ami  optici  are  injured 
(4).      Are  we  to  con- 
clude   from    this    that 
the  power  of  spontan- 
eous locomotion  is  lo- 
cated   in    the   thalami 
optici  ?   This  would  be  wrong,  for  if  the  whole  brain  of 
a  frog  including  the  pars  commissuralis  of  the  medulla 
oblongata  be  removed,  it  seems  ''  possessed  of  an  irre- 
sistible desire  to  move  ;  it  creeps  about  untiringly  in 
an  entirely  coordinated  manner  and  does  not  rest  until 
it  comes   to  a  corner  of  the  enclosure"  (Schrader). 
It  behaves  like  the  Nereis  in  Maxwell's  experiments 
which  was  deprived  of  its  brain.     Flourens  made  his 


Fig.  35.     The  Frog's  Brain. 

GH^  cerebral  hemispheres;  Th.Oy  thalamus  opticus; 
Lob.  opt^  lobi  optici ;  KH^  cerebellum  ;  V-XIy 
origin  of  the  5th  to  nth  brain-nerves.  (After 
Wiedersheim.) 


140    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

localisation  too  high  up.  We  wish  to  emphasise  the 
fact  that  the  frogs  from  which  Schrader  removed  the 
whole  brain,  including  the  pars  commissuralis,  not 
only  moved  but  were  still  able  to  climb.  The  con- 
dition of  rest  which  appears  after  injury  to  the  thala- 
mus is  thus  not  due  to  the  loss  of  spontaneity.  Steiner 
has  also  attempted  to  localise  locomotion  in  a  **  cen- 
tre." He  found  that  frogs  after  losing  the  pars  com- 
missuralis of  the  medulla  made  no  more  progressive 
movements,  and  concluded  from  this  that  the  sole 
and  undivided  control  over  all  locomotions  of  the  body 
belongs  to  this  part  (5  and  6).  Schrader's  contradic- 
tory results  overthrow  Steiner's  conclusions.  The 
latter  author  evidently  made  his  observations  on  mor- 
ibund animals,  for  his  frogs  survived  the  operation 
only  a  week  at  the  most,  while  Schrader's  lived  many 
months  and  entirely  recovered  from  the  operation. 

According  to  the  segmental  theory,  on  the  other 
hand,  it  is  to  be  expected  that  only  those  parts  of  the 
central  nervous  system  are  necessary  for  locomotion, 
which  correspond  to  the  segments  of  the  muscles  of 
the  arms  and  legs.  Thus  it  must  be  possible  to  ob- 
tain coordinated  locomotion  as  long  as  the  segmental 
ganglia  of  the  muscles  of  the  arms  and  legs  are  intact. 
This  agrees  with  the  result  obtained  by  Schrader 
that  after  extirpating  the  whole  brain,  including  the 
pars  commissuralis,  coordinated  locomotion  still  oc- 
curs. We  can  go  still  farther  and  extirpate  the  whole 
medulla  as  far  as  the  tip  of  the  calamus  scriptorius 
and  still  obtain  coordinated  locomotion.     **  Disturb- 


EXPERIMENTS  ON  VERTEBRATES  141 

ance  of  the  coordination  in  movements  first  begins  with 
the  apparent  decrease  in  the  ability  to  use  the  fore- 
legs, which  becomes  more  and  more  apparent  the 
nearer  the  incision  approaches  the  origin  of  the  bra- 
chial plexus  from  the  tip  of  the  calamus  scriptorius. 
When  this  is  reached  the  animal  falls  flat  on  its  belly  ; 
the  fore-legs  are  no  longer  able  to  carry  the  body.  If 
the  animal  be  stimulated  in  the  middle-line,  for  in- 
stance at  the  anus,  the  hind-legs  throw  the  body  for- 
ward. The  forward  extremities  participate  still  with 
*  alternating '  but  insufficient  and  peculiar  trembling 
movements.  A  really  coordinated  progressive  move- 
ment no  longer  takes  place."  We  see  again  in  this 
case  the  entire  validity  of  the  segmental  theory :  in- 
juries of  the  spinal  cord  in  the  vicinity  of  the  brachial 
plexus  interfere  with  the  walking  movements  only  in 
so  far  as  the  cooperation  of  the  fore-legs  comes  into 
consideration.  The  hind-legs,  on  the  other  hand, 
continue  to  function  normally.  Similar  phenomena 
may  be  observed  in  fishes.  They  also  cease  to  move 
about  when  the  brain  is  removed  up  as  far  as  the 
medulla  oblongata.  It  would  be  quite  wrong,  how- 
ever, to  conclude  from  this  that  the  centre  of  locomo- 
tion is  located  in  the  medulla  oblongata.  If  the  head 
of  a  shark  be  amputated  the  body  swims  about  spon- 
taneously. This  experiment  was  made  by  Steiner. 
From  the  standpoint  of  the  segmental  theory  this  re- 
sult was  to  be  expected.  The  tail  is  the  organ  of 
locomotion  for  the  shark,  and  only  the  corresponding 
segmental  ganglia  of  the  spinal  cord  are  required  for 


142    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

its  activity.  If  the  spinal  cord  of  a  young  salamander 
be  severed  the  swimming  movements  of  the  anterior 
and  posterior  parts  are  so  well  coordinated  that  it 
hardly  seems  credible  that  an  operation  has  been  per- 
formed. The  same  is  true  of  the  eel  (8).  The  con- 
ditions are  about  the  same  as  in  the  earthworm. 

Rubbing  the  back  of  the  frog  causes  it  to  croak,  and 
in  a  frog  whose  brain  has  been  removed  as  far  as 
the  medulla  oblongata,  this  sound,  as  Goltz  has 
found,  can  be  produced  with  machine-like  regularity 
(2).  Viewed  from  the  segmental  standpoint  this  reflex 
is  naturally  conditioned  by  the  integrity  of  the  me- 
dulla, since  it  is  there  that  the  motor  nerves  for  the 
production  of  the  voice  originate.  The  centre-theory 
had  found  a  supposed  **  centre  "  for  this  reflex  higher 
up  in  the  brain. 

4.  The  instinct  for  food  and  self-preservation  was, 
like  all  the  instincts,  located  in  the  cerebral  hemi- 
spheres. An  analysis  of  this  instinct  shows  that  it  is 
composed  of  several  reflexes,  which  are  discharged 
successively.  The  first  is  a  visual  reflex ;  the  frog 
catches  only  objects  (flies,  for  instance)  that  are  in 
motion.  The  opticus  ends  in  the  thalamus  opticus, 
hence  it  is  to  be  expected  that  the  loss  of  the  cerebral 
hemispheres  would  not  prevent  the  frog  from  catch- 
ing flies.  Schrader  found  this  to  be  the  case.  If 
previous  authors  believed  their  experiments  to  prove 
that  the  cerebral  hemispheres  are  necessary  for  see- 
ing, they  were  misled  by  the  shock-effects  of  the 
operation,  and  in  this  way  made  the  localisation  too 


EXPERIMENTS  ON  VERTEBRATES  143 

high.  Goltz  had  already  shown,  moreover,  that  the 
frog  deprived  of  its  cerebral  hemispheres  avoids  ob- 
stacles. The  same  holds  good  for  the  fish  that  has 
lost  the  cerebral  hemispheres.  The  first  act  in  taking 
food  thus  consists  in  an  optical  reflex.  As  soon  as 
the  food  comes  in  contact  with  the  palate  it  arouses 
swallowing  reflexes.  These  reflexes  are  completed 
by  means  of  the  vagus  group.  According  to  the 
segmental  theory  these  reflexes  should  still  be  possi- 
ble even  when  all  the  parts  of  the  brain  lying  in  front 
of  the  nuclei  of  the  vagus  have  been  removed.  Such 
is  the  case.  As  long  as  the  medulla  oblongata  is 
preserved  the  frog  swallows  the  food  that  is  put  into 
its  mouth. 

The  respiration  of  frogs  is  chiefly  mouth-  and  neck- 
respiration.  The  corresponding  nervous  segments 
for  these  parts  of  the  body  lie  in  the  medulla  oblon- 
gata and  in  the  beginning  of  the  spinal  cord.  If  the 
latter  be  severed  behind  the  nceud  vital  (calamus 
scriptorius),  as  Schrader  found,  all  the  muscles  whose 
nerves  originate  behind  the  place  of  division  continue 
to  participate  in  the  respiration  coordinately. 

It  was  formerly  assumed  that  the  compensatory 
movements  of  frogs  were  dependent  on  organs  of  the 
mid-brain.  Schrader  found,  however,  that  frogs 
whose  brain  had  been  extirpated  as  far  as  the  medulla 
oblongata  (the  origin  of  the  acusticus)  still  showed 
compensatory  movements.  The  earlier  physiologists 
were  deceived  by  accidental  effects  of  the  operation. 
For  the  sake  of  completeness  it  should  be  mentioned, 


144    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

further,  that  the  reflexes  of  wiping  and  warding  off 
objects  from  the  body  of  the  frog  are  of  a  purely 
segmental  character. 

We  have  now  given  a  review  of  the  principal  reac- 
tions of  the  frog  and  have  found  that  no  localisation 
of  functions  exists  either  in  the  brain  or  the  spinal 
cord,  that  these  are  only  segmental  reflexes,  just  as  in 
the  Annelids  and  Arthropods.  This  conception  was 
natural  after  results  obtained  from  experiments  on 
lower  animals.  That  Schrader  had  foreseen  it  before 
the  experiments  reported  here  were  known  is  proved 
by  the  closing  sentence  of  his  article  on  the  frog's 
brain  :  ""  The  series  of  experiments  we  have  given 
teaches  us  that  the  central  nervous  system  of  the  frog 
can  be  divided  into  a  series  of  sections,  each  of  which 
is  capable  of  performing  an  independent  function.  It 
brings  the  central  nervous  system  of  the  frog  into 
closer  relation  with  the  central  nervous  system  of  the 
lower  forms,  which  consists  of  a  series  of  distinct  gan- 
glia that  are  connected  by  commissures.  It  speaks 
against  the  absolute  monarchy  of  a  single  central  ap- 
paratus and  against  the  existence  of  different  kinds  of 
centres,  and  invites  us  to  seek  for  the  centralisation  in 
a  many-sided  coupling  of  relatively  independent  sta- 
tions." The  question  might  be  raised  as  to  whether 
the  activities  of  the  frog  which  we  have  considered 
include  all  the  reactions  of  this  animal.  The  more 
complicated  instincts  are  for  the  most  part  nothing 
more  than  series  of  segmental  reflexes.  I  am  inclined 
to  recommend  using  the  word  chain-reflexes,  whereby 


EXPERIMENTS  ON  VERTEBRATES  145 

the  performance  of  one  reflex  acts  at  the  same  time  as 
the  stimulus  for  setting  free  a  second  reflex.  The  tak- 
ing of  food  may  serve  as  an  illustration  of  such  a  chain- 
reflex.  The  optic  reflex  of  the  moving  fly  produces 
the  snapping  reflex  ;  the  contact  of  the  mouth-epi- 
thelium with  the  fly  produces  the  swallowing  reflex. 
Each  of  these  reflexes  is  purely  segmental.  By  tak- 
ing into  account  the  act  of  transmission,  complicated 
acts  can  thus  be  resolved  into  a  few  segmental 
reflexes.  A  second  fact  must  be  taken  into  consider- 
ation if  we  wish  to  trace  back  the  reactions  of  a  frog 
to  segmental  reflexes,  namely,  that  the  irritability  of 
the  organs  of  its  body  changes.  In  the  chapter  on 
instincts  we  shall  find  how  chemical  conditions,  espe- 
cially, affect  the  form  of  the  irritability  of  the  animal, 
and  how  all  conditions  which  bring  about  chemical 
changes  in  the  body  (temperature,  food,  sexual  pro- 
ducts) also  modify  its  irritability.  We  shall  then  un- 
derstand why  the  frog  burrows  at  the  beginning  of  the 
cold  weather  in  autumn  and  puts  in  an  appearance 
again  with  the  awakening  of  spring,  or,  strictly  speak- 
ing, with  the  beginning  of  the  warm  weather.  The 
segmental  reflex  in  the  frog  is,  however,  determined 
also  by  the  irritability  of  the  peripheral  organs  and  the 
arrangement  of  the  muscles.  The  segmental  ganglion 
acts,  in  the  main,  simply  as  the  protoplasmic  connec- 
tion between  the  surface  of  the  body  and  the  muscles. 
The  experiments  of  Goltz  and  of  Goltz  together 
with  Ewald  on  the  spinal  cord  of  dogs  prove  that  this 
law  of  segmental   reflexes  is    also  correct  for  dogs. 


146    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

However,  In  warm-blooded  animals  every  operation  in 
the  vicinity  of  the  medulla  oblongata  is  accompanied 
by  such  severe  shocks  to  the  segmental  respiratory 
ganglia  that  the  experimental  proof  is  still  wanting 
for  the  ganglia  of  the  medulla  in  higher  Vertebrates. 
It  has  been  attempted  with  electrical  stimuli,  but 
such  experiments  only  show  that  some  kind  of  proto- 
plasmic connection  exists  between  the  stimulated  spot 
and  the  segmental  ganglia  of  the  active  muscles.  The 
fact,  for  instance,  that  the  respiratory  movements  are 
affected  by  stimulation  of  the  third  ventricle  only 
proves  that  there  are  fibres  at  that  place  which  go  to 
the  segmental  respiratory  ganglia.  The  conclusion, 
however,  cannot  legitimately  be  drawn  from  this  that 
respiratory  ganglia  or  **  respiratory  centres"  are  located 
in  the  third  ventricle.  Two  facts  have  combined  to 
hinder  the  development  of  the  segmental  theory. 
First,  comparative  physiology  of  the  brain  and  embry- 
ology have  never  been  duly  considered.  Because  the 
brain  of  Vertebrates  only  reveals  its  segmental  char- 
acter in  the  earliest  embryological  condition,  only  a 
small  number  of  physiologists  have  thus  far  seriously 
believed  that  the  segmental  character  of  the  central 
nervous  system  would  furnish  the  key  for  comprehend- 
ing its  functions.  The  second  fact  is  disregard  of  the 
shock-effects  upon  those  parts  of  the  central  nervous 
system  situated  behind  the  seat  of  the  operation. 
It  Is  possible  that  certain  impulses  flow  constantly 
from  the  cephalic  to  the  lower  parts  of  the  central 
nervous  system.     The   stopping    of  these  Influences 


EXPERIMENTS  ON  VERTEBRATES  147 

causes  a  change  in  the  conditions  of  the  segmental 
ganglia  behind  the  seat  of  the  operation.  This  change 
is  the  shock-effect. 

Finally,  the  most  important  difference  between  the 
segmental  conception  of  the  central  nervous  system 
and  the  centre-theory  may  be  pointed  out.  Accord- 
ing to  the  latter  theory,  the  central  nervous  system 
consists  of  a  series  of  centres  for  as  many  different 
''functions."  Each  ** function"  is  determined  by  the 
structure  of  its  **  centre."  According  to  the  seg- 
mental theory,  there  are  only  indifferent  segmental 
ganglia  in  the  central  nervous  system,  and  the  dif- 
ferent reactions  or  reflexes  are  due  to  the  different 
peripheral  organs  and  the  arrangement  of  muscles. 
The  centre-theory  must  remain  satisfied  with  the 
mere  problem  of  localising  the  apparent  "  seat "  of  a 
"  function  "  without  being  able  to  give  the  dynamics 
of  the  reactions  of  an  animal,  as  the  latter  depend 
in  reality  upon  the  peripheral  structures,  and  not  on 
the  structures  of  the  ganglia.  For  this  reason  the 
segmental  theory  alone  will  be  able  to  lead  to  a 
dynamical  conception  of  the  functions  of  the  central 
nervous  system. 

This  difference  may  be  made  more  apparent  by 
comparison  of  these  functions  with  those  of  the  re- 
tina. The  optical  perception  of  forms  consists  in 
the  power  of  single  elements  to  determine,  accord- 
ing to  their  position  on  the  retina,  different  space- 
sensations.  One  retinal  element  may  aid  in  bringing 
about   many   different   pictures.     Viewed    from   the 


148    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

segmental  standpoint,  we  imagine  the  r6le  of  the 
central  nervous  system  to  be  similar  to  this :  the 
various  elements  or  ganglia  take  the  place  of  the  re- 
tinal elements  in  the  perception  of  forms.  The  same 
elements  or  ganglia  participate  in  many  "  functions." 
Every  element  shares  in  the  result  according  to  the 
location  of  the  segment,  and  other  general  or  special 
qualities.  But  if  we  attempt  to  make  clear  to  our- 
selves how  the  retina  should  act  according  to  the 
centre-theory,  we  find  that  every  retinal  element 
would  have  to  serve  for  the  perception  of  one  image 
only,  that  we  could  see  only  as  many  different  images 
as  we  have  retinal  elements  (for  instance,  rods).  We 
do  the  centre-theory  no  injustice  in  making  this  com- 
parison :  its  consistent  representatives  really  assume 
that  each  image  of  memory  is  deposited  in  a  special 
cell,  that  the  number  of  the  cells  of  the  brain  de- 
termines the  number  of  the  images  of  memory  which 
are  possible. 

I  wish  to  call  the  attention  of  the  reader  to  the  fact 
that  Dr.  A.  Meyer  has  arrived,  independently,  at  simi- 
lar conclusions  concerning  the  segmental  character  of 
the  central  nervous  system  of  Vertebrates  as  those  set 
forth  in  this  chapter  (9). 

Bibliography. 

1.  GOLTZ.  Ueber  die  Functionen  des  Lendenmarks  des  Hundes. 
Pfliiger's  Archiv,  Bd.  viii.,  1874. 

2.  GoLTZ.  Beitrdge  zur  Lehre  von  den  Nervencentren  des 
Frosches.     Berlin,  1868.     Verlag  von  Hirschwald. 


EXPERIMENTS  ON  VERTEBRATES         149 

3.  Flourens,  p.  Recherches  expirimentales  sur  les  Propriitis  et 
les  Eonctions  du  Systeme  Nerveux,  etc.     2.  edit.     Paris,  1842. 

4.  SCHRADER,  Max  E.  G.  Zur  Physiologie  des  Eroschgehirns. 
Pflugers  Archiv,  Bd.  xli.,  1887. 

5.  Steiner,  J.  Die  Eunctionen  des  Centralnervensy stems  und 
ihre  Phylogenese.  Erste  Abtheilung :  Untersuchungen  iiber  die 
Physiologie  des  Eroschhirns.     Braunschweig,  1885. 

6.  Steiner,  J.  Die  Eunctionen  des  Centralnervensystems  und 
ihre  Phylogenese.  II.  Abtheilung,  Die  Eische,  Braunschweig, 
1888. 

7.  GoLTZ,  Fr.,  and  Ewald,  J.  R.  Der  Hund  mit  verkiirztem 
Rilckenmark.     Pfluger's  ArchiVy  Bd.  Ixiii.     Bonn,  1896. 

8.  BiCKEL.  Beitrdge  zur  Riickenmarksphysiologie  des  Aales. 
Pfliiger's  Archiv,  Bd.  Ixviii. 

9.  Meyer,  Adolf.  Critical  Review  of  the  Data  and  General 
Methods  and  Deductions  of  Modern  Neurology.  Journal  of  Com- 
parative Neurology y  vol.  viii.,  1898. 


CHAPTER   X 

SEMIDECUSSATION  OF  FIBRES  AND   FORCED 
MOVEMENTS 

It  is  apparent  from  the  foregoing  that  in  the  central 
nervous  system  of  Vertebrates  only  segmental  gan- 
glia and  only  segmental  reflexes  appear.  Superior 
centres,  a  "centre  of  coordination"  for  instance,  can- 
not exist.  Irritability  and  conductivity  suffice  to  pro- 
duce coordination  in  Medusae,  in  the  heart,  in  the 
respiration  of  Limulus,  and  in  the  movements  of  the 
earthworm  and  the  salamander.  Schrader  has  rightly 
expressed  it :  the  nature  of  the  nervous  connections 
alone  determines  the  cooperation  of  different  seg- 
ments in  a  common  activity.  Some  of  these  connec- 
tions require  special  mention,  for  instance,  those  in 
which  decussation  and  semidecussation  of  fibres  ap- 
pear. Possibly  the  most  familiar  example  of  semi- 
decussation is  found  in  the  optic  nerves.  Here  the 
fibres  cross,  so  that  while  each  eye  has  its  own  special 
nerve  each  tract  contains  fibres  from  both  eyes.  The 
fibres  of  the  temporal  half  of  the  retinae  pass  through 
the  chiasma  uncrossed  (that  is,  remain  on  the  same 
side  of  the  head  and  brain),  the  fibres  which   come 

150 


FORCED  MOVEMENTS  151 

from  the  nasal  side  of  the  retinae  undergo  a  decussa- 
tion, i.  e.,  they  cross  to  the  other  side  of  the  head  and 
brain.  The  left  optic  tract  contains  fibres  from  the 
temporal  side  of  the  left  eye,  and  from  the  nasal, 
or  internal,  side  of  the  right  eye.  If  the  left  tract  be 
cut,  the  left  sides  of  both  retinae  become  blind,  and 
the  patient  recognises  nothing  more  in  the  right  half 
of  the  field  of  vision.     This  is  a  case  of  hemianopia. 

A  similar  semidecussation  also  occurs  in  the  motor 
nerves  of  the  eye.  For  the  time  being  we  may  con- 
sider the  various  muscles  of  each  eye  as  a  unit.  In 
the  lateral  movements  of  our  eyes  the  rectus  externus 
of  one  eye  and  the  rectus  internus  of  the  other  co- 
operate. If  we  assume  an  inherited  connection  be- 
tween the  retinal  elements  and  the  movements  of  the 
eyes,  the  right  externus  and  the  left  internus  must  be 
innervated  by  the  left  half  of  the  brain.  The  nerve- 
fibres  of  the  externi  must  thus  be  crossed,  those  of 
the  interni  not  crossed.  The  semidecussation  in  this 
case  naturally  occurs  in  the  brain,  and  not  peripherally. 
The  pathological  expression  of  this  motor  semidecus- 
sation is  the  deviation  conjugde^  which  is  a  motor 
affection,  corresponding  to  the  sensory  affection, 
hemianopia.  We  can  only  expect  to  find  these 
semidecussations  where  symmetrical  organs  always 
receive  equal  innervations,  as  in  the  case  of  our  eyes. 
Our  arms  and  legs  can  move  independently  of  each 
other,  but  in  lower  Vertebrates  the  case  is  different. 
The  symmetrical  fins  of  the  fish  receive  equal  innerv- 
ations.     I   have   shown    that  associated  changes  of 


152    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

position  of  the  eyes  and  fins  can  be  produced  by  de- 
struction of  an  ear  or  the  acoustic  nerve  (i).  If  we 
destroy  in  a  shark  the  left  auditory  nerve  or  the  left 
side  of  the  medulla,  where  the  auditory  nerve  enters, 
the  left  eye  of  the  animal  looks  down,  the  right  up. 
This  change  of  position  of  both  eyes  suggests  that 
the  relative  tension  between  the  muscles  that  raise 
the  eyes  has  changed.  In  the  left  eye  the  tension  of 
the  lowering  muscles  predominates  over  that  of  their 
antagonists  ;  in  the  right  eye  the  reverse  is  the  case. 
The  fins,  likewise,  show  associated  changes  of  posi- 
tion. The  left  fin  is  raised  dorsally,  the  right  is  bent 
ventrally.  While  it  can  be  said  that  both  eyes  are 
rolled  about  the  longitudinal  axis  of  the  animal  toward 
the  left,  the  fins  are  rolled  about  the  same  axis  to  the 
right.  Although  the  pectoral  fins  show  the  associated 
changes  of  position  most  clearly,  these  changes  also 
exist  in  all  the  remaining  fins,  only  with  the  difference 
that  the  amount  of  the  change  of  position  decreases 
the  farther  the  segment  is  removed  from  the  point  of 
operation.  The  influence  of  the  operation  must  de- 
crease as  the  distance  of  a  ganglion  increases.  The 
resistance  to  the  transmission  of  the  change  increases 
with  the  distance. 

These  observations  enable  us  to  draw  a  conclusion 
concerning  the  connection  of  the  muscles  with  the 
right  and  left  halves  of  the  corresponding  ganglia. 
We  may  assume  that  a  permanent  decrease,  but  not  a 
permanent  increase  in  the  tension  of  the  muscles  can 
result  from  the  destruction  of  one  part  of  the  brain. 


FORCED  MOVEMENTS  153 

It  is  thus  the  muscles  directly  or  indirectly  connected 
with  the  left  side  of  the  medulla  oblongata  (in  the 
acoustic  segment)  which  show  a  decrease  in  tension 
after  the  destruction  of  the  left  ear.  Accordingly,  the 
left  side  of  the  medulla  is  connected  with  the  raising 
muscles  of  the  left  eye  and  the  lowering  muscles  of 
the  right  eye,  as  well  as  with  the  lowering  muscles  of 
the  left  pectoral  fin  and  the  raising  muscles  of  the 
right  pectoral  fin.  If  we  start  with  the  idea  that  all 
the  muscles  of  an  eye  or  a  fin  form  a  common  whole, 
a  kind  of  semidecussation  is  present.  It  is,  however, 
not  only  the  muscles  of  the  fins  that  undergo  such 
changes  of  tension,  but  probably  also  the  muscles  of 
the  spinal  column. 

If  the  symmetrical  muscles  of  the  organs  of  loco- 
motion possess  different  tension,  the  usual  stimuli  for 
locomotion  must  naturally  lead  to  unsymmetrical  in- 
stead of  symmetrical  movements.  When  the  lower- 
ing muscles  predominate  in  the  right  pectoral  fin  and 
the  raising  muscles  in  the  left,  the  animal,  when  these 
fins  are  used,  will  come  under  the  influence  of  a  couple 
of  forces  which  must  produce  a  rolling  movement 
around  the  longitudinal  axis  of  its  body  toward  the 
left.  As  long  as  the  animal  swims  slowly,  rolling  mo- 
tions do  not  occur,  for  they  are  compensated  for. 
The  friction  of  the  fish  in  the  water  will  suffice  to 
destroy  a  slight  rolling  motion.  But  if  the  animal 
attempts  to  swim  rapidly,  e,  g.,  if  it  be  excited,  it  be- 
gins to  roll.  These  rolling  motions  are  called  forced 
movements,  a  poorly  selected  term.     The  same  move- 


154    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

ments  have  also  been  noticed  in  dogs  and  rabbits 
after  an  operation  on  one  side  of  the  medulla. 

If  a  fish  whose  progressive  movements  are  deter- 
mined by  the  sculling  motions  of  the  tail  turns  to  the 
right,  the  tail  moves  with  greater  force  toward  the 
right  than  toward  the  left.  This  condition  might  be 
made  permanent  if  it  were  possible  to  weaken  the 
muscles  on  the  left  side  of  the  spinal  column.  This 
occurs  when  the  right  side  of  the  acoustic  segment  of 
the  medulla  is  destroyed.  The  fish  moves  in  a  circle 
toward  the  right.  We  also  obtain  circus-motions  to- 
ward the  right  if  we  destroy  the  ventral  portion  of  the 
left  optic  lobe.  Hence,  fibres  must  pass  from  the 
ventral  portion  of  the  left  optic  lobe  to  the  right 
acoustic  segment  of  the  medulla.  After  such  an 
operation,  an  increase  in  the  tension  of  the  skeletal 
muscles  occasionally  shows  itself,  for  the  fish  may  lie 
permanently  bent  into  a  circle  without  being  able  to 
straighten  itself  out  again.^  Such  a  fish  can  no  longer 
swim  straight  ahead.  The  difference  in  the  tension 
of  the  muscles  on  the  two  sides  of  the  animal  is,  how- 
ever, usually  not  so  great,  in  which  case  the  circus- 
motions  will  appear  only  spasmodically,  for  ex;ample, 
when  the  animal  is  excited. 

One-sided  division  of  the  spinal  cord  and  of  the 
medulla  behind  the  acoustic  segment  produces  no 
forced  movements  (2  and  3).     On  the  other  hand,  roll- 

*  If  such  a  fish  be  decapitated  the  curvature  of  the  body  remains.  It  may 
even  remain  after  death.  We  have  to  deal  with  an  organic  change  in  the 
muscles,  caused  by  the  operation. 


FORCED  MOVEMENTS  155 

ing  and  circus-motions  may  occur  after  injury  to  the 
brain  in  front  of  this  segment,  wherever  places  are 
met  with  which  are  directly  or  indirectly  connected 
with  the  acoustic  segment.  This  is  the  case,  for  in- 
stance, after  a  one-sided  lesion  of  the  pons  or  the 
cerebral  hemispheres  in  rabbits  and  dogs.  In  both 
animals  circus-motions  occur  after  destruction  of  the 
cerebral  hemispheres,  in  rabbits  toward  the  intact  side, 
in  dogs  toward  the  injured  side.  All  the  facts  prove 
that  the  semidecussations  take  place  in  the  vicinity  of 
the  acoustic  segment  and  not  farther  down.  In  man, 
so  far  as  I  know,  circus-motions  have  never  been  ob- 
served ;  this  is  probably  due  to  his  upright  walk.  It 
would  be  interesting  to  make  the  experiment  of  having 
patients  afflicted  with  certain  diseases  (for  instance, 
diseases  of  the  inner  ear)  walk  on  all  fours  (with 
closed  eyes)  and  to  observe  whether  circus-motions 
occur. 

As  we  have  already  mentioned,  it  is  a  well-known 
fact  that  in  Arthropods  after  destruction  of  one  half 
of  the  supracesophageal  ganglion  circus-motions  can 
occur.  That  they  need  not  occur  has  been  shown  by 
Miss. Hyde  and  also  by  Bethe  (4  and  5).  According 
to  the  investigations  of  the  latter  author  these  circus- 
motions  in  Invertebrates  are  called  forth  by  very  dif- 
ferent disturbances  in  the  muscle-tension.  It  is  often 
due  simply  to  a  disturbance  in  the  muscle-tension  of 
the  extremities  of  one  side,  the  other  side  being  ap- 
parently normal.  In  Crustaceans,  associated  changes 
of  position  of  the  extremities  can  also  occasionally 


156    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 


occur  after  destruction  of  one  half  of  the  supraoesoph- 
ageal  ganglion.      In  Cephalopods  von   Uexkiill  has 

observed  forced 
movements  after 
lesion  of  an  ear. 
Fig.  36  shows  the 
predominance  of 
the  flexors  of  the 
legs  over  the  ex- 
tensors on  the  left 
side  of  the  body  of 
a  Limulus.  In  this 
animal  the  right 
half  of  the  brain 
had  been  de  - 
stroyed  and  it 
showed  circus-mo- 
tions toward  the 
left. 

Steiner  has  made 
a  peculiar  applica- 
tion of  the  facts  of 
forced  movements. 
He  imagines  that 
the  ability  to  move 
forward  is  a  spe- 
cific "function"  of 
the  brain,  and  has  believed  that  it  would  be  possible  by 
means  of  this  criterion  to  decide  whether  or  not  a  gan- 
glion of  a  lower  animal  should  be  called  a  brain.     The 


Fig.  36. 


FORCED  MOVEMENTS  157 

facts  of  comparative  physiology  do  not  favour  this  con- 
ception. Spontaneous  progressive  movements  exist 
in  Infusoria  which  possess  no  nervous  system,  and  even 
in  plant  organisms,  for  example,  in  the  swarmspores 
of  algae.  It  is  an  important  principle  of  physiological 
epistemology  that  a  phenomenon  which  occurs  gener- 
ally, cannot  possibly  be  the  specific  function  of  an 
organ  which  is  peculiar  to  a  few  forms  only.  Steiner 
soon  found  a  fact  that  showed  the  erroneousness  of 
his  theory,  the  fact  that  the  decapitated  shark  con- 
tinues to  swim  about  in  the  tank.  Schrader  had  like- 
wise found  that  the  frog  without  a  brain  is  still  able  to 
perform  spontaneous  progressive  movements.  Steiner 
maintains  further  that  *'  the  brain  is  defined  by  the 
general  centre  of  movement  in  connection  with  the 
action  of  at  least  one  of  the  higher  sensory  nerves." 
''  In  addition  to  its  great  simplicity  this  definition  has 
still  another  advantage,  namely,  that  it  is  satisfied  by  a 
single  experiment ;  because  of  the  two  elements  of 
which  the  definition  is  made  up,  one  element  is  always 
given  anatomically.  This  is  the  higher  sensory  nerve, 
whose  presence  also  vouches  for  its  function.  The 
one  experiment  that  it  is  necessary  to  make  has  to 
prove  that  in  addition  to  the  sensory  apparatus  the  gen- 
eral centre  of  movement  also  exists.  The  proof  is  then 
complete  if  the  one-sided  removal  of  the  central  nerv- 
ous part  so  changes  the  direction  of  the  movements 
of  the  animals  that  a  circus-motion,  which  is  generally 
known  by  the  name  forced  movement,  takes  the  place 
of  a   forward  movement"   (Steiner).      This  idea  is 


158    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

likewise  erroneous  and  easily  leads  to  absurdity.  One- 
sided destruction  of  the  cerebral  hemispheres  in  man 
produces  no  forced  movements.  Thus,  according  to 
Steiner,  the  cerebral  hemispheres  should  not  be- 
long to  the  brain.  Second,  according  to  Steiner, 
the  ear  must  be  a  brain.  One-sided  lesion  of  the 
ear  is  sure  to  produce  forced  movements  in  a  series 
of  animals,  and,  moreover,  the  auditory  nerve  is  a 
higher  sensory  nerve.  I  have  mentioned  this  sub- 
ject at  this  place  because  it  is  a  typical  illustration  of 
what  plays  on  words  in  physiology  lead  to.  It  is 
not  our  task  to  find  a  definition  for  the  word  brain, 
but  to  gain  an  insight  into  the  functions  of  the  central 
nervous  system.  It  is  of  minor  importance  what 
name  we  give  to  the  different  parts  of  the  central 
nervous  system. 

In  connection  with  this  chapter  we  wish  to  call  at- 
tention to  the  more  recent  experiments  of  Sherring- 
ton and  H.  E.  Hering,  from  which  it  seems  to  follow 
that  with  the  innervation  of  a  muscle  the  relaxation  of 
its  antagonist  results  simultaneously. 

Bibliography. 

1.  LoEB,  J.  Ueber  Geotropismus  bei  Thieren.  Pfluger's  Archiv^ 
Bd.  xlix.,  189 1. 

2.  LoEB,  J.  Ueber  den  Antheil  des  Hornerven  an  den  nach 
Gehirnverletzung  auftretenden  Zwangsbewegungen,  Zwangslagen 
und  associirten  Stellungsdnderungen  der  Bulbi  und  Extremitdten. 
Pfluger's  ArchiVy  Bd.  1.,  189 1. 

3.  Steiner.  Die  Functionen  des  Centralnervensystems  und  ihre 
Phylogenese.     II.  Die  Fische.     Braunschweig,  1888. 


¥ 


FORCED  MOVEMENTS  159 

4.  Bet  HE,  A.  Vergleichende  Untersuchungen  uber  die  Func- 
tionen  des  Centralnervensystems  der  Arthropoden.  P Auger's  Ar- 
chiVy  Bd.  Ixviii.,  1897. 

5.  Bethe,  a.  Das  Centralnervensystetn  von  Carcinus  mcenas. 
II.  Mittheil.     Arch.  f.  mikroskop.  Anatomie^  Bd.  1.,  1897. 

6.  Steiner,  J.  Die  Functionen  des  Centralnervensystems  wir- 
belloser  Thiere.  Sitzungsberichte  der  Berliner  Akademie  der  Wis- 
senschaften.     1890,  I.  S.,  39. 


CHAPTER   XI 


RELATIONS  BETWEEN  THE  ORIENTATION  AND 
E UNCTION  OF  CERTAIN  ELEMENTS  OF  THE 
SEGMENTAL  GANGLIA 

The  results  of  some  investigations  carried  on  by 
Garrey  and  myself  showed  that  if  a  constant  current 
be  sent  through  a  trough  in  which  are  larvae  of 
Amblystoma,  peculiar  changes  may  be  observed  in 
the  postures  of  the  animals  (i).  If  the  current  passes 
through  them  longitudinally  from  head  to  tail  (Fig. 
37)  the  back  becomes  convex  and  the  ventral  side 


Fig.  37.    Attitude  of  an  Amblystoma  under  the  Influence  of  a 
Galvanic  Current  Passing  from  Head  to  Tail. 


Fig.  38.    Attitude  of  an  Amblystoma  when  the  Galvanic  Cur- 
rent Passes  from  Tail  to  Head. 

concave.  This  change  of  position  is  occasioned  by 
the  muscles  of  the  ventral  side  (the  flexors  of  the 
spinal  column)  becoming  more  tense  than  the  dorsal 

160 


ORIENTATION  AND  FUNCTION  i6i 

muscles  (the  extensors  of  the  spinal  column)  from  the 
passage  of  the  current.  On  the  other  hand,  if  the 
current  goes  through  the  animal  in  the  direction  from 
tail  to  head  both  head  (Fig.  38),  and  tail  are  raised. 
The  body  becomes  more  concave  on  the  dorsal  side 
and  convex  on  the  ventral  side.  The  extensors  of  the 
spinal  column  become  more  tense  than  the  ventral 
muscles.  A  pronounced  opisthotonus  exists.  In 
order  to  show  the  phenomenon  clearly  the  animal 
must  be  brought  into  the  current  gradually.  If 
we  continue  to  raise  the  intensity  of  the  current, 
changes  of  position  also  take  place  in  the  legs.  The 
changes  in  the  hind-legs  are  more  easily  described 
than  those  in  the  fore-legs.  If  the  current  passes  from 
head  to  tail  the  hind-legs  are  braced  backward  (Fig. 
-^f),  making  the  forward  movement  (to  the  anode) 
easier.  If  the  current  passes  from  tail  to  head  the 
hind-legs  are  braced  forward  (Fig.  38),  making  the 
backward  movement  (to  the  anode)  easier.  How  can 
these  phenomena  be  explained  ?  The  current  has  two 
kinds  of  effects.  A  conduction  of  the  current  takes 
place  through  ions.  Wherever  the  progress  of  ions  is 
blocked  in  the  central  nervous  system,  an  increase  in 
their  concentration  will  occur  and  this  must  be  followed 
by  physical  or  chemical  alterations  of  the  colloids.  The 
progress  of  ions  may  be  blocked  by  semipermeable 
membranes  at  the  external  limit  of  neurons  or  some- 
where inside  the  neurons.  Wherever  anions  are 
blocked  different  effects  (anelectrotonus)  will  be  pro- 
duced than  at  places  where  the  progress  of  kations  is 


i62    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

blocked  (katelectrotonus).  The  action  of  the  various 
ions  on  nerve-elements  is  as  yet  unknown.  The  other 
effect  of  the  current  may  consist  in  the  migration  of 
certain  colloids  in  one  direction  and  of  water  in  the 
other  direction. 

If  in  the  larvse  of  Amblystoma  the  tension  of  the 
flexors  of  the  spinal  column  predominates  in  a  de- 
scending current  (from  head  to  tail)  and  the  tension 
of  the  extensors  of  the  spinal  column  predominates  in 
an  ascending  current,  this  proves  that  the  nervous  ele- 
ments of  the  flexors  and  extensors  in  the  central  7ier- 
vous  system,  which  are  afl^ected  by  the  ions,  possess  an 
opposite  orie7itation.  Maxwell  and  I  have  developed 
more  definite  ideas  concerning  the  orientation  of  these 
elements,  but  such  details  are  for  the  time  being  of 
minor  importance.  I  only  wish  to  state  that  the  rela- 
tive orientation  of  these  elements  must  be  the  same 
in  every  segment  of  the  spinal  cord  ;  for  when  the 
spinal  cord  in  the  larvse  of  Amblystoma  is  severed  or 
the  whole  animal  cut  into  several  pieces  the  effects 
of  the  current  remain  the  same.  Since  the  article 
mentioned  above  was  published  I  have  found  that 
crayfish  (young  and  small  specimens  were  used  for 
these  experiments)  behave  toward  the  current  like 
Amblystoma  larvae.  If  the  median-plane  of  the 
crayfish  is  in  the  direction  of  the  lines  of  the  current 
(which  are  all  straight  and  parallel  in  these  experi- 
ments) and  the  head  is  turned  toward  the  anode,  the 
flexors  of  the  body  contract  and  the  crayfish  rolls  it- 
self into  a  complete  ring,  provided  that  the  density  of 


ORIENT  A  TION  AND  F  UNCTION  163 

the  current  is  exactly  right.  The  back  is  convex,  the 
ventral  side  concave.  But  if  the  current  passes  from 
tail  to  head,  the  back  becomes  entirely  straight,  the 
extensors  being  contracted  to  the  utmost  limit.^  The 
dorsal  side  cannot  become  concave  because  the  exo- 
skeleton  of  the  crayfish  does  not  allow  it.  Thus  in 
the  body  of  the  crayfish  the  motor  elements  of  the 
extensors  and  flexors  which  are  affected  by  the  cur- 
rent must  have  the  same  orientation  as  in  the  body  of 
Vertebrates.  This  holds  good  not  only  for  the  flexors 
and  extensors  of  the  body  but  generally,  as  we  shall 
at  once  see. 

We  have  already  mentioned  the  fact  that  a  con- 
stant current  passing  through  Amblystoma  larvae  in 
the  longitudinal  direction  affects  not  only  the  tension 
of  the  flexors  and  extensors  of  the  body,  but  also 
the  muscles  of  the  extremities.  The  tension  too  is 
changed  in  such  a  way,  as  has  been  already  intimated, 
that  it  renders  movement  toward  the  anode  easy, 
movement  toward  the  kathode  difficult.  If,  for  in- 
stance, the  current  passes  through  the  animal  from 
head  to  tail  the  hind-legs  are  braced  backward  and 
the  position  of  the  fore-legs  is  changed  correspond- 
ingly, so  that  the  progressive  movement  of  the  ani- 
mal is  made  easy,  the  backward  movement  dif- 
ficult. If,  however,  the  current  passes  from  tail  to 
head  the  hind-legs  are  braced  forward  and  the  posi- 
tion of  the  fore-legs  is  changed  correspondingly  ;  the 

'  It  is  necessary  that  in   this  experiment  the  intensity  of  the  current  be 
increased  very  slowly. 


i64    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

animal  can  go  backwards  easily,  while  forward  move- 
ment is  difficult.  In  fact  it  is  apparent  that  if  the 
animals  attempt  to  move  in  any  direction  while 
the  current  is  passing  through  them  they  go  toward 
the  anode.  ^ 

From  this  fact  it  follows  that,  for  the  nervous  appa- 
ratus of  the  progressive  movements  of  Amblystoma,  a 
close  relation  must  exist  between  the  orientation  of 
the  determinative  elements  of  the  motor  nerves  and 
their  function  :  in  fact  the  nervous  elements  which 
cause  the  progressive  movements  must  have  with  re- 
gard to  the  longitudinal  direction  of  the  animal  an 
orientation  which  is  opposite  to  the  orientation  of 
those  elements  which  cause  the  backward  movement. 
Garrey  and  I  had  called  attention  to  the  fact  that  the 
observations  of  Blasius  and  Schweitzer  show  that 
other  Vertebrates,  for  instance,  young  eels,  behave 
like  Amblystoma.  The  same  also  holds  good  for  the 
shrimp.  This  last  assertion  is  based  upon  a  series  of 
experiments  made  by  Maxwell  and  myself  (2).  These 
experiments  were  made  chiefly  on  Palaemonetes.  This 
Crustacean  uses  the  third,  fourth,  and  fifth  pairs  of  legs 
for  its  locomotion.  The  third  pair  pulls  in  the  for- 
ward movement  and  the  fifth  pair  pushes.  The  fourth 
pair  generally  acts  like  the  fifth  and  requires  no  further 
attention.  If  a  current  be  sent  through  the  animal 
longitudinally,  from  head  to  tail,  and  the  strength  in- 
creased gradually,  a  change  soon  takes  place  in  the 

^  This  explains  the  galvanotropic  gatherings  observed  by  Hermann,  Blasius 
and  Schweitzer,  and  others. 


ORIENTATION  AND  FUNCTION  165 

position  of  the  legs.  In  the  third  pair  the  tension 
of  the  flexors  predominates,  in  the  fifth  the  tension  of 
the  extensors.  The  animal  can  thus  move  off  easily 
with  the  pulling  of  the  third  and  the  pushing  of  the 
fifth  pairs  of  legs,  that  is  to  say,  the  current  changes 
the  tension  of  the  muscles  in  such  a  way  that  the 
forward  movement  is  rendered  easy,  the  backward 
difficult.  Hence  it  can  easily  go  tow^ard  the  anode, 
but  only  with  difficulty  toward  the  kathode.  If  a 
current  be  sent  through  the  animal  in  the  opposite  di- 
rection, namely,  from  tail  to  head,  the  third  pair  of  legs 
is  extended,  the  fifth  pair  bent ;  that  is,  the  third  pair 
can  push  and  the  fifth  pair  pull.  The  animal  will 
thus  go  backward  easily  and  forward  with  difficulty. 
We  see  here  again  that  the  nervous  elements  of  the 
central  nervous  system  which  bring  about  the  for- 
ward movements  have  the  opposite  orientation  as  re- 
gards the  longitudinal  axis  of  the  animal  from  the 
nervous  elements  which  bring  about  the  backward 
movement.  But  we  can  go  still  further  in  the  devel- 
opment of  this  law.  Palaemonetes  can  not  only  walk, 
but  is  also  a  good  swimmer,  and  it  can  swim  back- 
wards as  well  as  forwards.  In  swimming  forwards 
the  swimming  appendages,  among  which  the  tail  fin 
must  be  counted,  push  backwards  forcibly  and  for- 
wards gently ;  in  swimming  backwards  the  opposite 
occurs.  If  the  current  be  sent  through  Palaemonetes 
in  the  direction  from   head  to    tail  ^   the   swimming 

'  The  tail  fin  behaves  toward  the  current  like  the  abdominal  swimming  ap- 
pendages and  not  like  the  body.  This  must  be  taken  into  consideration  in 
galvanotropic  experiments. 


i66  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

appendages,  and  the  tail  also,  are  stretched  backward 
or  dorsad  to  their  fullest  extent.  This  proves  that  the 
tension  of  the  muscles  that  move  those  organs  back- 
wards is  greater  than  that  of  their  antagonists.  The 
shrimp  can  thus  swim  forwards  toward  the  anode 
easily  under  the  influence  of  such  a  current,  but  back- 
wards only  with  difficulty.  If  the  current  passes 
through  in  the  opposite  direction  (from  tail  to  head), 
however,  the  tail  and  the  ventral  appendages  are 
turned  forward.  The  tension  and  the  development 
of  energy  now  predominate  in  those  muscles  which 
move  the  swimming  appendages  backwards.  In  this 
way  the  animal  can  swim  backwards  easily,  while  it  is 
difficult  or  impossible  for  it  to  swim  forwards.  Hence 
the  nervous  elements,  which  determine  the  forward- 
swimming,  must  also  have  the  same  orientation  in  re- 
gard to  the  longitudinal  axis  of  the  animal  as  those 
elements  which  determine  the  walking  forwards,  while 
the  nervous  elements  for  swimming  backwards  have 
the  opposite  orientation. 

The  fact  yet  remains  to  be  considered  that  Palae- 
monetes,  like  many  other  Crustacea,  can  also  move 
sideways.  This  movement  is.produced  by  the  pulling 
of  the  legs  on  the  side  toward  which  the  animal  is 
moving  (contraction  of  the  flexors),  while  the  legs  of 
the  other  side  push  (contraction  of  the  extensors). 
If  a  current  be  sent  transversely,  say  from  right  to 
left,  through  the  animal,  the  legs  of  the  right  side 
assume  the  flexor-position,  those  of  the  left  side  the 
extensor-position.     In  the  legs  of  the  right  side  the 


ORIENTATION  AND  FUNCTION  167 

flexors  produce  more  energy,  in  the  legs  of  the  left 
side  the  extensors.  The  transverse  current  assists  the 
animal  in  moving  to  the  right  toward  the  anode  and 
prevents  it  from  moving  to  the  left  toward  the  kath- 
ode. Hence  the  nervous  elements  which  produce 
the  sidewise  movement  of  the  crayfish  toward  the 
right  must  have  the  opposite  orientation  in  regard  to 
the  longitudinal  axis  from  the  nervous  elements  which 
produce  the  sidewise  movement  to  the  left. 

Maxwell  and  I  had  attempted  to  give  a  picture  of 
the  arrangement  of  those  elements  on  the  assumption 
that  they  are  the  motor  neurons.  No  reason  exists, 
however,  for  regarding  the  ganglion-cell  in  toto  as  the 
point  of  action  for  the  chemical  effect  of  the  ions  set 
free.  It  may  be  any  element  inside  of  the  ganglion- 
cells,  or  even  of  the  fibre  itself ;  it  is  not  even  neces- 
sary that  this  element  should  be  especially  noticeable 
histologically.  Life-phenomena  are  determined  by 
physical  and  chemical  conditions  which  are  outside  the 
realm  of  histology.  But  whatever  it  is,  it  is  certain 
that  those  determinative  elements  in  the  central  ner- 
vous system  whose  activity  produces  movements  of  the 
body^  have  a  fixed  orientation  in  the  body,  which  evi- 
dently stands  in  some  simple  relation  to  the  direction  of 
the  movem^ent  which  is  produced  by  it. 

The  idea  of  such  a  simple  relation  between  the 
orientation  of  nervous  elements  and  the  direction  of 
motion  produced  by  them  is  no  more  strange  than 
the  facts  observed  in  the  stimulation  of  the  horizon- 
tal canal  of  the  labyrinth.     If  this  canal  be  slightly 


i68    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

touched  motions  of  the  eyes  or  head  occur  in  the  plane 
of  this  canal.  In  this  case  we  have  to  deal  with  a  sim- 
ple relation  between  the  orientation  of  the  canal  and 
the  plane  in  which  the  organs  or  the  whole  body  of 
the  animal  move.  This  fact  is  just  as  mysterious 
as  the  more  general  facts  mentioned  in  this  chapter.  I 
am  inclined  to  assume  that  the  peculiar  relation  be- 
tween the  semicircular  horizontal  canal  and  the  motions 
produced  by  the  stimulation  of  this  canal  finds  its 
explanation  through  the  facts  mentioned  in  this  chap- 
ter. It  is  possible  that  the  central  endings  of  the 
nerve  of  the  horizontal  canal  are  connected  with  the 
motor  elements  in  the  medulla  whose  activity  pro- 
duces motions  in  the  plane  of  the  horizontal  canal. 
When  Flourens  made  his  experiments  on  the  semi- 
circular canals  he  found  that  there  was  a  striking 
resemblance  between  the  effects  of  a  destruction  of 
the  canals  and  the  sectioning  of  the  crura  cerebelli. 
He  came  to  the  conclusion  that  there  must  be  a  sim- 
ple relation  between  the  direction  of  the  fibres  of  the 
crura  cerebelli  and  the  motion  produced  by  them  (3). 
His  observations  are  not  in  all  points  correct ;  yet 
with  some  modification  his  fundamental  idea  remains 
true.  The  next  chapter,  on  the  cerebellum,  will  give 
us  some  more  data  about  his  observations. 

It  is  possible  for  us  to  conceive  from  this  how  it 
happens  that  the  same  optic  stimulus  or  the  same 
space-perception  is  able  to  direct  our  eyes  toward  a 
certain  point,  to  turn  our  head  in  that  direction,  to 
guide  our  finger  thither,  or  to  bring  our  legs  into  such 


ORIENT  A  TION  AND  FUNCTION  169 

activity  that  our  body  arrives  at  that  place.  It  is 
possible  that  the  elements  of  the  central  nervous  system 
which  become  active  in  this  way  all  have  the  same  ori- 
entation in  each  segment^  and  what  we  call  an  innerva- 
tion may  be  a  process  in  which  the  orientation  of  the 
elements  plays  a  role.  The  effect  of  the  electric  cur- 
rent might  be  an  example  of  such  a  process.  This 
problem  of  the  physiology  of  coordinated  movement 
which  we  touch  upon  here  has  always  seemed  to  me 
the  most  mysterious  in  the  whole  physiology  of  the 
central  nervous  system,  and  the  way  offered  here  of 
reaching  a  simple  solution  seems  to  me  worthy  of 
mention.  The  whole  conception  can  easily  be  classified 
under  the  segmental  conception  of  the  central  nervous 
system.  Movements  of  the  eyes,  head,  arms,  and  legs 
depend  upon  as  many  different  segmental  ganglia. 
Each  of  these  ganglia  has  some  features  in  common 
with  every  other  ganglion,  for  instance  the  orientation 
and  arrangement  of  the  elements  (neurons?).  If  a 
process  of  such  a  nature  that  it  can  only  stimulate 
elements  oriented  in  a  certain  way  in  each  ganglion 
spreads  through  the  segmental  ganglia,  it  must  pro- 
duce a  movement  in  exactly  the  same  direction  in  the 
appendages  of  each  segment.  This  does  away  with 
the  necessity  of  imagining  artificial  connections  of  the 
neurons  which  would  be  able  to  produce  such  a  series  of 
coordinated  motions  in  different  limbs  and  segments. 

If  the  question  be  raised,  however,  as  to  how  it 
happens  that  a  simple  relation  exists  between  the 
orientation    of   the   motor    nerve-elements    and   the 


170  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

movement  or  progressive  movement  produced  by 
them,  we  must  again  refer  to  the  simple  segmental 
relations  of  the  first  embryonic  formation  that  re- 
mains better  preserved  in  the  central  nervous  system 
than  in  the  muscles.  The  problem  with  which  we  have 
to  deal  here  is  ultimately  a  problem  of  embryology. 

Bibliography. 

1.  LoEB,  J.,  and  Walter  E.  Garrey.  Zur  Theorie  des  Gal- 
vanotropismus.  II.  Mittheilung.  Versuche  an  Wirbelthieren.  Pflil- 
ger's  Archiv^  Bd.  Ixv.,  1896. 

2.  LoEB,  J.,  and  S.  S.  Maxwell.  Zur  Theorie  des  Galvanotro- 
pismus.     Pfluger's  Archiv,  Bd.  Ixiii.,  1896. 

3.  Flourens,  p.     Fonctions  du  Syst^me  nerveux.     Paris,  1842. 


[ 


CHAPTER   XII 

EXPERIMENTS  ON  THE  CEREBELLUM 

The  experiments  on  the  cerebellum  support  to  a 
certain  extent  the  observations  mentioned  in  the 
preceding  chapter. 

The  cerebellum,  like  the  cerebral  hemispheres,  is 
a  structure  which  clearly  expresses  inequality  of 
growth.  Both  may  be  considered  as  evaginations 
and  appendages  of  the  segmental  nervous  system. 
The  cerebellum  is  connected  with  the  central  nervous 
system  by  three  crura,  the  crura  cerebelli  ad  medullam 
oblongatam,  the  crura  cerebelli  ad  pontem,  and  the 
crura  cerebelli  ad  corpora  quadrigemina.  The  latter 
extend  forward  in  a  pretty  straight  line,  the  first  ex- 
tend backward,  and  the  peduncles  to  the  pons  at  right 
angles  to  both.  Magendie  discovered  and  Flourens 
confirmed  the  fact  that  lesion  of  these  tracts  possess- 
ing so  characteristic  an  orientation  to  the  chief  axes 
of  the  body  produces  **  forced  "  movements  whose  di- 
rection bears  a  simple  relation  to  the  orientation  of 
the  severed  peduncle.  If  a  peduncle  of  the  pons 
be  severed  on  one  side  the  animal  rolls  about  its 
longitudinal  axis.  If  the  crura  cerebelli  that  extend 
forward  be  severed  the  ^nimal  rushes  forward  with 

171 


I 


172  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

great  force  ;  if  the  crura  cerebelli  ad  medullam  ob- 
longatam  be  severed  the  animal  goes  backwards  or 
shows  a  tendency  to  turn  somersaults  backwards. 
'*  La  direction  des  mouvements  produits  par  la  section 
des  fibres  de  I'encephale  est  done  toujours  determinee 
par  la  direction  de  ces  fibres"  (Flourens). 

Flourens  called  attention  to  the  analogy  of  these 
phenomena  with  those  he  observed  after  lesion  of  the 
semicircular  canals.  This  analogy,  however,  does  not 
exist  just  as  he  states  it.  He  compares  the  effect  of 
the  one-sided  division  of  the  pons  with  the  division 
of  a  horizontal  canal.  This  is  not  correct.  So  far 
as  I  know,  such  a  lesion  does  not  produce  rolling  mo- 
tions about  the  longitudinal  axis  in  any  animal.  On 
the  other  hand,  destruction  of  a  whole  ear,  probably 
in  most  cases,  causes  rolling  motions.  Flourens 
states  further  that  after  destruction  of  the  anterior 
canals  an  animal  turns  somersaults  forwards,  after  de- 
struction of  the  posterior  canals  backwards.  Flourens 
assumes  that  the  nerves  of  the  three  canals  continue 
into  the  corresponding  peduncles  of  the  cerebellum, 
and  that  this  origin  of  the  nerves  is  the  cause  of  the 
phenomena  that  we  observe  after  lesion  of  the  single 
semicircular  canals  (3).  But  this  is  probably  not  cor- 
rect, since  the  auditory  nerve  ends  in  the  medulla.  It 
is  possible,  however,  that  the  cerebellum  is  connected 
with  the  same  motor  elements  in  the  medulla  with 
which  the  acoustic  nerve  is  connected.  The  cerebel- 
lum might  thus  appear  as  an  appendage  of  the  acous- 
tic segments. 


EXPERIMENTS  ON  THE  CEREBELLUM      173 

This  harmonises  with  the  results  Ferrier  obtained 
from  his  stimulation  experiments  (i).  He  found  that 
stimulation  of  the  different  parts  of  the  cerebellum 
causes  associated  movements  of  the  eyes,  and  that 
the  direction  of  the  movement  changes  with  the  posi- 
tion of  the  electrodes.  The  head  also  moves  in  the 
same  direction  as  the  eyes.  Movements  of  the  limbs 
were  also  observed,  but  it  could  not  be  determined 
whether  or  not  they  were  associated  with  the  move- 
ments of  the  head.  From  this  we  may  conclude  that 
possibly  or  probably  the  movements  which  are  pro- 
duced by  stimulation  of  the  cerebellum  are  somewhat 
related  to  those  movements  which  are  produced  by 
stimulation  or  injury  of  the  semicircular  canals,  only 
that  the  stimulation  experiments  on  the  cerebellum, 
according  to  Ferrier,  often  yield  no  results. 

Extirpation  of  the  cerebellum  leaves  the  sensory 
and  psychic  functions  of  the  animal  undisturbed.  It 
is  only  in  the  movements  that  peculiar  disturbances 
appear,  which  are  described  differently  by  the  differ- 
ent authors.  The  motions  of  the  animals  resemble 
somewhat  those  of  a  patient  suffering  from  St.  Vitus's 
dance,  inasmuch  as  they  do  not  reach  the  intended 
aim  and  are  often  excessive  in  character.  It  is  neces- 
sary that  the  head  of  a  dog  whose  cerebellum  has  been 
injured  be  held  in  the  dish  when  it  eats,  for  if  not  held 
every  effort  sends  the  head  so  much  too  far  that  the 
animal  is  not  able  to  get  its  food.  This  disturbance 
is  most  pronounced  immediately  after  the  operation 
and  may  disappear  more  or  less  after  a  certain  time. 


174  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

Such  disturbances  also  show  themselves  in  the 
limbs.  The  animal  often  staggers  about  like  an  in- 
toxicated person  and  finds  difficulty  in  keeping  itself 
on  its  legs.  All  these  peculiarities  perhaps  point  ul- 
timately to  a  decrease  in  the  tension  of  the  skeletal 
muscles.  The  measured  movements  of  the  normal 
animal  are  only  possible  if  the  tension  of  the  antag- 
onistic muscles  is  so  great  that  excessive  movements 
cannot  take  place.  But  if  the  muscles  of  the  spinal 
column  are  relaxed  in  the  dog  without  the  cerebellum, 
as  has  been  maintained  (and  apparently  with  good 
reason),  every  intended  movement  can  go  wide  of  its 
aim. 

According  to  the  results  of  Luciani's  numerous 
experiments,  weakness  or  relaxation  of  the  muscles 
seems  to  form  the  most  constant  factor  in  the  effects  of 
operations  on  the  cerebellum.  The  affected  groups 
of  muscles,  however,  seem  to  vary  with  the  position 
of  the  part  of  the  cerebellum  which  is  destroyed. 
Flourens,  who  attributed  special  functions  to  each  sec- 
tion of  the  brain,  maintained  that  the  cerebellum  was 
the  general  centre  of  coordination,  because  lesions  of 
the  cerebellum  bring  about  the  above-mentioned  dis- 
turbances. Luciani  (2)  has  shown,  however,  that 
some  of  the  dogs  that  had  lost  the  cerebellum  were 
still  able  to  perform  coordinated  swimming  motions 
in  the  water  and  even  coordinated  walking  motions. 
The  weakness  of  all  or  of  certain  groups  of  muscles 
may  lead  to  ataxic  disturbances,  but  in  some  cases 
these  may  be  very  slight.    Thus  we  see  that  Flourens's 


EXPERIMENTS  ON  THE  CEREBELLUM      175 

theory  that  the  cerebellum  is  an  organ  of  coordination 
is  not  correct.  It  may  be  too  that  a  part  of  the  dis- 
turbances observed  after  lesion  of  the  cerebellum  are 
due  to  secondary  effects  of  the  operation  on  the  med- 
ulla or  the  corpora  quadrigemina. 

This  latter  conception  is  supported  by  comparative 
physiology.  In  fishes  and  frogs,  in  which  the  shock- 
effects  are  slight,  the  cerebellum  can  be  removed 
without  producing  any  disturbance  in  the  behaviour 
of  the  animals  (Vulpian,  Steiner).  In  sharks,  whose 
cerebellum  is  strongly  developed,  I  myself  have  made 
numerous  division-experiments  and  numerous  experi- 
ments on  partial  or  total  extirpation  of  the  cerebel- 
lum, and  no  change  whatever  took  place  in  the 
behaviour  of  the  anirnals.  It  is  impossible  and  un- 
justifiable in  this  case  to  talk  of  a  definite  "  function  " 
of  the  cerebellum. 

It  may  be  well,  in  consideration  of  what  has  been 
said  in  the  preceding  chapter  and  of  observations 
which  will  be  discussed  later  on  concerning  the  results 
of  lesions  of  the  cerebral  hemispheres,  to  remind  the 
reader  of  a  hypothesis  made  by  Magendie.  He  saw 
animals  walk  or  fly  backwards  permanently  after  les- 
ion of  a  certain  part  of  the  medulla  oblongata.  He 
saw  further  that  a  lesion  of  the  corpora  striata  pro- 
duces an  impulse  to  run  forwards.  Finally  he  ob- 
served the  rolling  motions  of  the  animals  about  their 
longitudinal  axis  after  one-sided  lesion  of  the  pons. 
He  makes  the  following  remark  in  this  connection : 
*'  Comme  notre  esprit  a  besoin  de  s'arr^ter  ^  certaines 


176    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

images  je  dirai  qu'il  existe  dans  le  cerveau  quatre  im- 
pulsions spontanees  ou  quatre  forces  qui  seraient  pla- 
cees  aux  extremites  de  deux  lignes,  qui  se  couperaient 
a  angle  droit,  Tune  pousserait  en  avant,  la  deuxieme  en 
arriere,  la  troisieme  de  droit  a  gauche  en  faisant  rouler 
le  corps,  la  quatrieme  de  gauche  a  droite  en  faisant 
executer  un  mouvement  semblable  de  rotation.  Dans 
les  diverses  experiences  d'ou  je  tire  ces  consequences 
les  animaux  deviennent  des  especes  d'automates  mon- 
tes  pour  executer  tels  ou  tels  mouvements  et  incap- 
ables  d'en  produire  aucun  autre."  The  last  statement 
goes  too  far,  but  Magendie's  main  thought  deserves 
more  consideration  than  it  has  heretofore  received 
from  physiologists.  The  galvanotropic  facts  men- 
tioned in  Chapter  XI.  show  most  conclusively  that  in 
Crustaceans  and  Vertebrates  there  exists  a  relation 
between  the  orientation  and  function  of  certain  motor 
elements,  and  a  similar  relation  also  finds  expression  in 
the  experiments  on  the  horizontal  semicircular  canal.^ 

'  Dr.  Lyon  has  shown  that  only  the  stimulation  of  the  horizontal  canal  gives 
rise  to  motions  in  the  plane  of  this  canal,  while  the  same  result  cannot  be  ob- 
tained with  any  degree  of  certainty  through  a  stimulation  of  the  two  other 
canals  (4). 

Bibliography. 

1.  Ferrier.      The  Functions  of  the  Brain.     New  York,  1886. 

2.  LuciANi,    LuiGi.     Das   Kleinhirn.     Leipzig,   1893. 

3.  Flourens,  p.     Fonctions  du  Systlme  nerveux.     Paris,  1842. 

4.  Lyon,  E.  P.  A  Contribution  to  the  Comparative  Physiology 
of  Compensatory  Motions.  The  American  Journal  of  Physiology^ 
vol.  iii.,  1900. 


CHAPTER   XIII 

ON   THE   THEORY  OE  ANIMAL  INSTINCTS 

I.  The  discrimination  between  reflex  and  instinctive 
actions  is  chiefly  conventional.  In  both  cases  we  have 
to  deal  with  reactions  to  external  stimuli  or  conditions. 
But  while  we  speak  of  reflex  actions  when  only  a 
single  organ  or  a  group  of  organs  react  to  an  external 
stimulus,  we  generally  speak  of  instincts  when  the 
animal  as  a  whole  reacts.  In  such  cases  the  reactions 
of  the  animal,  although  unconscious,  seem  often  to  be 
directed  towards  a  certain  end.  A  fly  acts  instinct- 
ively when  it  lays  its  ^gg  on  objects  which  serve 
the  hatching  larvae  as  food.  We  call  the  periodical 
migrations  of  animals  instinctive.  We  call  it  instinct- 
ive when  certain  animals  conceal  themselves  in  cracks 
and  crevices  where  they  are  safe  from  persecution. 
But  the  purposeful  character  of  instincts  cannot  be 
used  to  distinguish  them  from  reflexes,  as  a  great 
many  of  the  reflexes  are  also  purposeful,  for  instance, 
the  closing  of  the  eyelid  if  the  conjunctiva  be  touched 
or  the  wiping  off  of  acetic  acid  that  is  put  on  the 
skin  of  a  decapitated  frog.  On  the  other  hand,  it 
cannot  be  said  that  every  instinctive  action  is  purpose- 


178  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

ful,  for  instance,  the  flying  of  the  moth  into  the 
flame. 

In  many  cases  the  greater  complication  of  instinctive 
actions  compared  with  simple  reflex  actions  is  due  to  the 
fact  that  in  the  instinctive  actions  we  have  to  deal 
with  a  chain  of  reflexes  in  which  the  first  reflex  be- 
comes at  the  same  time  the  cause  which  calls  forth 
the  second  reflex.  The  taking  up  of  food  by  the 
frog  is  a  good  illustration  of  this.  The  motion  of  the 
fly  causes  an  optical  reflex  which  results  in  the  snap- 
ping motion.  The  contact  of  the  fly  with  the  mucous 
membrane  of  the  pharynx  sets  free  a  second  reflex,  the 
swallowing  reflex,  which  brings  the  fly  into  the  oeso- 
phagus. If  it  be  true  that  the  instincts  belong  to  the 
same  class  of  processes  as  the  reflexes,  their  relation  to 
the  central  nervous  system  should  be  the  same.  We 
have  seen  that  as  far  as  reflexes  are  concerned,  the 
nervous  system  only  acts  as  a  protoplasmic  conductor 
between  the  periphery  (sense  organs)  and  the  muscles. 
I  think  it  is  possible  to  show  that  this  is  also  true  for 
instincts.  In  order  to  prove  this,  we  shall  have  to  go 
into  an  analysis  of  the  instincts.  We  shall  select  for 
our  analysis  such  simple  cases  of  instincts  as  depend 
upon  tropisms. 

2.  We  have  seen  that  when  certain  Crustaceans,  for 
instance  Palaemonetes,  are  subjected  to  the  effect  of  a 
galvanic  current  such  changes  of  tension  take  place  in 
the  muscles  of  the  appendages  that  movement  toward 
the  anode  becomes  easier,  and  toward  the  kathode 
more  difficult.     The  result  is  that  if   the  current  is 


b 


THEORY  OF  INSTINCTS  179 

continued  long  enough,  all  the  animals  collect  at  the 
positive  pole.  When  this  process  is  observed  with- 
out a  careful  analysis,  it  seems  as  though  these  Crus- 
taceans possessed  the  instinct  to  move  toward  the 
anode,  just  as  the  moths  possess  the  instinct  to  move 
into  the  flame.  The  flight  of  the  moth  into  the  flame 
is  in  reality  only  the  result  of  a  tropism, — heliotropism, 
which  differs  from  galvanotropism  chiefly  in  that  the 
rays  of  light  take  the  place  of  the  curves  of  the  current. 
The  reader  knows  that  certain  plants  when  exposed 
to  the  light  on  one  side,  for  instance,  when  cultivated 
at  a  window,  bend  their  tip  toward  the  window  until 
the  tip  of  the  stem  is  in  the  direction  of  the  rays 
of  light.  The  tip  then  continues  to  grow  in  the 
direction  of  the  rays.  We  call  this  dependence  of 
orientation  on  light  heliotropism.  We  speak  of 
positive  heliotropism  when  the  organ  bends  towards 
the  source  of  light,  of  negative  heliotropism  when 
the  organ  bends  away  from  it.  It  is  generally 
assumed  that  the  light  has  a  chemical  effect  in  these 
cases. 

The  relations  of  symmetry  in  plants  and  animals 
play  an  important  part  in  these  phenomena.  We 
will  take,  by  way  of  illustration,  the  stem  of  a 
hydroid,  Eudendrium  that  is  being  raised  near  a  win- 
dow. I  have  found  that  it  bends  toward  the  window 
like  a  positively  heliotropic  plant  under  the  same' 
conditions.  The  process  may  be  described  as  follows  : 
The  light  strikes  the  Eudendrium-stem  from  the 
side.     A  contraction  of  the  protoplasm  on  that  side 


i8o  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

ensues  and  a  greater  resistance  is  thus  offered  to  the 
increase  in  length  on  this  side  than  on  the  opposite 
side.  The  result  is  that  the  stem  bends  and  becomes 
concave  on  the  side  toward  the  light.  As  soon,  how- 
ever, as  the  bending  has  progressed  so  far  that  the 
stem  comes  into  the  direction  of  the  rays  of  light,  all 
the  symmetrical  elements  are  struck  by  the  light  at 
the  same  angle.  The  intensity  of  light  is  thus  equal 
at  symmetrical  points,  and  there  is  no  longer  occasion 
for  the  stem  to  leave  this  direction.  It  thus  con- 
tinues to  grow  in  the  direction  of  the  rays  of  light. 
Negatively  heliotropic  elements,  roots,  for  instance, 
differ  from  positively  heliotropic  elements  in  that  the 
light  produces  a  relaxation  of  the  protoplasm.  Hence 
when  the  light  comes  from  one  side,  the  resistance  to 
the  growth  on  that  side  will  be  less  than  on  the  op- 
posite side,  and  the  tip  will  bend  away  from  the 
source  of  light.  As  soon  as  the  tip  comes  into  the 
direction  of  the  rays  of  light  and  the  symmetrical 
points  are  all  struck  by  them  at  the  same  angle,  the 
intensity  of  the  light  on  both  sides  is  the  same,  and 
every  cause  for  leaving  this  direction  is  removed.  It 
has  been  known  for  a  long  time  that  many  animals 
are  "  attracted  "  by  the  light  and  fly  into  the  flame. 
This  was  considered  a  special  instinct.  It  was  said 
that  these  animals  loved  the  light,  that  curiosity 
drove  them  into  it.  I  have  shown  in  a  series  of 
articles,  the  first  of  which  appeared  in  January,  1888, 
that  all  these  actions  are  only  instances  of  those  phe- 
nomena which  were  known  in  plants  as  heliotropism. 


THEORY  OF  INSTINCTS  i8i 

It  was  possible  to  show  that  the  heliotropism  of 
animals  agreed  in  every  point  with  that  of  plants. 
If  a  moth  be  struck  by  the  light  on  one  side,  those 
muscles  which  turn  the  head  toward  the  light  become 
more  active  than  those  of  the  opposite  side,  and 
correspondingly  the  head  of  the  animal  is  turned 
toward  the  source  of  light.  As  soon  as  the  head  of 
the  animal  has  this  orientation  and  the  median-plane 
(or  plane  of  symmetry)  comes  into  the  direction  of 
the  rays  of  light,  the  symmetrical  points  of  the  sur- 
face of  the  body  are  struck  by  the  rays  of  light  at  the 
same  angle.  The  intensity  of  light  is  the  same  on 
both  sides,  and  there  is  no  more  reason  why  the 
animal  should  turn  to  the  right  or  left,  away  from  the 
direction  of  the  rays  of  light.  Thus  it  is  led  to 
the  source  of  the  light.  Animals  that  move  rapidly 
(like  the  moth)  get  into  the  flame  before  the  heat  of 
the  flame  has  time  to  check  them  in  their  flight. 
Animals  that  move  slowly  are  affected  by  the  increas- 
ing heat  as  they  approach  the  flame  ;  the  high  tem- 
perature checks  their  progressive  movement  and  they 
walk  or  fly  slowly  about  the  flame.  The  more  re- 
fractive rays  are  the  most  effective  in  animals  just  as 
in  plants  (i). 

Hence  the  "  instinct"  that  drives  animals  into  the 
light  is  nothing  more  than  the  chemical — and  indirect- 
ly the  mechanical — effect  of  light,  an  effect  similar  to 
that  which  forces  the  stem  of  the  plant  at  the  window 
to  bend  toward  the  source  of  light,  or  which  forces 
Palaemonetes  to  collect  at  the   anode.      The   moth 


1 82    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

does  not  fly  into  the  flame  out  of  '*  curiosity,"  neither 
is  it  **  attracted  "  by  the  Hght ;  it  is  only  oriented  by  it 
and  in  such  a  manner  that  its  median-plane  is  brought 
into  the  direction  of  the  rays  and  its  head  directed 
toward  the  source  of  light.  In  consequence  of  this 
orientation  its  progressive  movements  must  lead  it  to 
the  source  of  light. 

We  now  come  to  the  most  important  question  in 
this  chapter,  namely,  the  relation  of  the  central 
nervous  system  to  the  instincts.  As  long  as  such 
apparently  complex  things  as  the  instincts  are  not 
analysed  but  treated  as  entities,  it  is  easy  to  believe 
that  they  are  based  upon  very  mysterious  nervous 
structures.  It  would  harmonise  with  the  centre- 
theory  to  assume  for  the  moth  a  '*flying-into-the- 
flame  centre,"  ^  and  to  seek  for  its  localisation  in  the 
central  nervous  system.  The  fact  that  the  flying  of 
the  moth  into  the  flame  is  nothing  but  positive  helio- 
tropism,  and  the  fact  that  the  positive  heliotropism  of 
animals  is  identical  with  the  positive  heliotropism  of 
plants,  proves  that  this  reaction  must  depend  upon 
conditions  which  are  common  to  animals  and  plants. 
Plants,  however,  possess  no  central  nervous  system, 
therefore  I  believe  that  it  is  impossible  for  the  helio- 
tropic  reactions  of  animals  to  depend  upon  specific 
structures  of  the  central  nervous  system.     It  is  much 

*Steiner  tries  indeed  to  "explain"  the  righting  motions  of  the  starfish  by 
the  assumption  of  a  "righting  centre  "  in  the  central  nervous  system.  He 
does  not  consider  the  possibility  that  contact  stimuli  and  the  irritable  structures 
at  the  periphery  may  be  sufficient  for  this  reaction,  and  that  the  nerves  act 
only  as  protoplasmic  conductors  between  the  skin  and  the  muscles. 


THEORY  OF  INSTINCTS  183 

more  probable  that  they  are  determined  by  properties 
which  are  common  to  animals  and  plants.  From  what 
has  been  said  above  it  is  easy  to  infer  what  these 
properties  are  :  First,  heliotropic  animals  as  well  as 
heliotropic  plants  must  contain  a  substance  on  their 
surfaces  which  undergoes  a  chemical  change  when 
subjected  to  the  influence  of  the  light,  and  this  change 
must  be  able  to  produce  changes  of  tension  in  the 
contractile  tissue.  Second,  heliotropic  animals  as 
well  as  heliotropic  plants  possess  symmetry  of  form 
and  a  corresponding  distribution  of  the  irritabilities. 
These  two  groups  of  conditions  determine  the  helio- 
tropic reaction  unequivocally.  But  what  has  the 
central  nervous  system  to  do  with  this  **  instinct  "  of 
the  moth  to  fly  into  the  flame,  or,  as  we  may  now 
say,  with  its  heliotropism  ?  I  believe  nothing  more 
than  that  the  nervous  system  contains  a  series  of 
segmental  ganglia  which  establish  the  protoplasmic 
connection  between  the  skin  and  muscles.  If  we 
destroy  the  central  nervous  system,  the  heliotropic 
reactions  in  many  animals  cease,  but  mainly  for  the 
reason  that  the  connection  between  the  skin,  or  the 
eyes,  which  are  affected  by  the  light,  and  the  muscles, 
is  interrupted.  Hence  it  would  be  just  as  wrong  to 
assume  a  specific  centre  for  the  flight  of  the  moth 
into  the  flame  as  it  would  to  assume  a  specific  centre 
for  the  going  of  Palsemonetes  to  the  anode. 

3.  We  will  select  another  instinct,  namely,  the 
habit  many  animals  have  of  crawling  into  cracks  and 
crevices.      This  "  instinct "  is  very  prevalent  in  the 


i84    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

animal  kingdom,  especially  among  insects,  worms,  etc. 
This  is  called  an  instinct  of  self-preservation,  and  it 
is  assumed  that  the  animal  thus  escapes  from  its 
pursuers.  The  centre  theory  would  assume  a  special 
centre  for  this  instinct.  This  is,  however,  only  an- 
other instance  of  a  simple  tropism.  Many  plants 
and  animals  are  forced  to  orient  their  bodies  in  a  cer- 
tain way  toward  solid  bodies  with  which  they  come  in 
contact.  I  have  given  this  kind  of  irritability  the 
name  stereotropism.  Like  the  positive  and  negative 
heliotropism  and  geotropism,  there  is  also  a  positive 
and  negative  stereotropism,  and  there  are  also  stereo- 
tropic  curvations.  I  have  found,  for  instance,  that 
when  a  Tubularia  is  brought  in  contact  with  a  solid 
body,  the  polyp  and  the  growing  tip  bend  away  from 
the  body  while  the  stolon  sticks  to  it.  The  polyp 
is  negatively  stereotropic  and  the  stolon  positively 
stereotropic.  Stereotropism  plays  a  very  important 
part  in  the  processes  of  pairing  and  the  formation  of 
organs.  The  tendency  of  many  animals  to  creep 
into  cracks  and  crevices  has  nothing  to  do  with  self- 
concealment,  but  only  with  the  necessity  of  bringing 
the  body  on  every  side  in  contact  with  solid  bodies. 
I  have  proved  this,  for  instance,  in  a  peculiar  species 
of  butterfly,  Amphipyra,  that  is  a  fast  runner.  As 
soon  as  free,  it  runs  about  until  it  finds  a  corner  or  a 
crack  into  which  it  can  creep.  I  placed  some  of  these 
animals  in  a  box,  one  half  of  which  was  covered  with 
a  non-transparent  body,  the  other  half  with  glass.  I 
covered   the   bottom   of   the   box   with   small   glass 


I 


THEORY  OF  INSTINCTS  185 

plates  which  rested  on  small  blocks,  and  were  raised 
just  enough  from  the  bottom  to  allow  an  Amphipyra 
to  get  under  them.  Then  the  Amphipyra  collected 
under  the  little  glass  plates,  where  their  bodies  were 
in  contact  with  solid  bodies  on  every  side,  not  in  the 
dark  corner  where  they  would  have  been  concealed 
from  their  enemies.  They  even  did  this  when  in  so 
doing  they  were  exposed  to  direct  sunlight.  This  re- 
action also  occurred  when  the  whole  box  was  dark.  It 
was  then  impossible  for  anything  but  the  stereotropic 
stimuli  to  produce  the  reaction.  The  same  phenom- 
enon may  be  observed  in  worms,  for  instance,  in 
Nereis.  If  an  equal  number  of  Nereis  and  glass  tubes 
be  placed  in  a  dish  of  sea- water,  we  may  be  sure 
that  after  a  time  we  shall  find  a  worm  in  each  tube. 
This  even  occurs  when  the  tubes  are  exposed  to  the 
direct  rays  of  the  sun,  which  kill  the  worms.  This  is 
also  a  reaction  which  is  common  to  plants,  hydroids, 
and  animals  possessing  a  central  nervous  system, 
which  must  therefore  depend  upon  circumstances 
which  have  nothing  directly  to  do  with  the  central 
nervous  system.  These  circumstances  are  apparently 
chemical  effects  in  the  skin,  which  are  produced  in 
these  forms  by  the  contact  with  solid  bodies.  This  is 
another  instance  where  the  central  nervous  system 
only  plays  the  part  of  a  protoplasmic  conductor.  It 
would  be  entirely  wrong  to  attempt  to  look  for  a 
'*  centre  of  self-concealment  "  in  these  animals.  This 
is  confirmed  by  experiments  on  worms  that  have  been 
cut  into  pieces. 


1 86  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

4.  We  will  now  turn  our  attention  to  the  consider- 
ation of  some  more  complicated  instincts.  It  always 
seemed  to  me  one  of  the  most  wonderful  arrange- 
ments in  nature  that,  in  many  species,  the  female  lays 
her  eggs  in  places  where  the  newly  born  larvae  find 
just  the  kind  of  food  they  require.  The  fly  lays  its 
eggs  on  decaying  meat,  cheese,  or  similar  material, 
and  it  is  on  these  substances  that  the  young  larvae 
feed.  I  have  often  placed  pieces  of  lean  meat  and 
pieces  of  fat  from  the  same  animal  side  by  side  on 
the  window-sill,  but  the  fly  never  failed  to  lay  its  eggs 
on  the  meat  and  not  on  the  fat.  I  further  tried  to 
raise  the  larvae  on  fat.  As  was  to  be  expected,  they 
did  not  grow,  but  soon  died.  It  was  possible  to  dis- 
cover the  mechanics  of  the  peculiar  instincts  of  the 
mothers  through  experiments  on  the  young  larvae. 
The  larvae  are  oriented  by  certain  substances  which 
radiate  from  a  centre,  and  this  orientation  takes  place 
in  the  same  way  as  in  the  orientation  of  heliotropic  ani- 
mals by  the  light.  The  centre  of  diffusion  takes  the 
place  of  the  source  of  light,  and  the  lines  of  diffusion 
(that  is  the  straight  lines  along  which  the  molecules 
move  from  the  centre  of  diffusion  into  the  surrounding 
medium — i.  e.,  the  air)  the  place  of  the  rays  of  light. 
The  chemical  effects  of  the  diffusing  molecules  on 
certain  elements  of  the  skin  influence  the  tension  of 
the  muscles,  as  the  rays  of  light  influence  the  tension 
of  the  muscles  in  heliotropic  animals.  The  orienta- 
tion of  an  organism  by  diffusing  molecules  is  termed 
chemotropism,  and  we  speak  of  positive  chemotropism 


THEORY  OF  INSTINCTS  187 

when  the  animal  Is  forced  to  bring  Its  axis  of  symme- 
try into  the  direction  of  the  lines  of  diffusion  and  to 
turn  its  head  toward  the  centre  of  diffusion.  In 
such  an  orientation  every  pair  of  symmetrical  points 
on  the  surface  of  the  animal  is  met  by  the  lines  of 
diffusion  at  the  same  angle.  It  can  easily  be  shown 
that  larvae  of  the  fly  are  positively  chemotropic  toward 
certain  chemical  substances  which  are  formed,  for 
Instance,  in  decaying  meat  and  cheese,  but  which  are 
not  contained  in  fat.  The  substances  in  question 
are  probably  volatile  nitrogenous  compounds.  The 
young  larvae  are  probably  led  by  those  substances  to 
the  centre  of  diffusion  in  the  same  way  as  the  moth 
into  the  flame.  The  female  fly  possesses  the  same 
positive  chemotropism  for  these  substances  as  the 
larvae,  and  is  accordingly  led  to  the  meat.  As  soon 
as  the  fly  is  seated  on  the  meat,  chemical  stimuli  seem 
to  throw  into  activity  the  muscles  of  the  sexual  or- 
gans, and  the  eggs  are  deposited  on  the  meat.  It 
may  also  be  possible  that  at  the  time  when  the  fly  Is 
ready  to  deposit  Its  eggs  the  positive  chemotropism 
is  especially  strongly  developed.  It  is  only  certain 
that  neither  experience  nor  volition  plays  any  part  in 
these  processes.  If  the  question  be  raised  as  to  what 
is  necessary  in  order  to  produce  these  reactions,  the 
answer  is,  first,  the  presence  of  a  substance  in  the  skin 
or  certain  parts  of  the  skin  (sense-organs)  of  the  ani- 
mal which  is  altered  by  the  above-mentioned  volatile 
substances  contained  in  the  decaying  meat,  and 
second,  the  bilateral  symmetry    of   the   body.     The 


i88  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

central  nervous  system  plays  no  other  role  in  this  than 
that  it  forms  the  protoplasmic  bridge  for  the  conduc- 
tion from  the  skin  to  the  muscles.  In  organisms  in 
which  this  conduction  is  possible  without  a  central 
nervous  system,  in  plants,  for  instance,  we  also  find 
the  same  reactions. 

5.  We  find  another  instance  of  a  preservative  in- 
stinct in  the  young  caterpillars  of  many  butterflies. 
The  larvae  of  Porthesia  chrysorrhoea  creep  out  of  the 
eggs  in  the  autumn  and  winter  in  colonies  in  a  nest  on 
trees  or  shrubs.  The  warm  spring  sun  drives  them 
out  of  the  nest  and  they  crawl  up  on  the  branches  of 
the  tree  or  shrub  to  the  tip,  where  they  find  their  first 
food.  After  having  eaten  the  tips,  they  crawl  about 
until  they  find  new  buds  or  leaves,  which  in  the  mean- 
time have  come  out  in  great  numbers.  It  is  evident 
that  the  instinct  of  the  caterpillars  to  crawl  upwards, 
as  soon  as  they  awake  from  the  winter  sleep,  saves 
their  lives.  Were  they  not  guided  by  such  an  in- 
stinct, those  that  crawled  downwards  would  die  of 
starvation.  What  r6le  does  the  central  nervous  sys- 
tem play  in  these  instincts  ? 

I  have  found  that  the  young  caterpillars  of  Por- 
thesia are  oriented  by  the  light.  Until  they  have 
taken  food  they  are  positively  heliotropic.  This 
positive  heliotropism  leads  them  to  the  tips  of  the 
branches  where  they  find  their  food.  During  the  win- 
ter they  are  stiff  and  do  not  move.  The  higher  tem- 
perature of  the  spring  brings  about  chemical  changes  in 
their  bodies,  and  these  chemical  processes  cause  them 


THEORY  OF  INSTINCTS  189 

to  move.  But  the  direction  of  their  movements  is 
determined  by  the  light.  Out-of-doors,  where  the 
diffused  light  strikes  the  animal  on  all  sides,  every  ray 
of  light  can  be  resolved  into  a  horizontal  and  a  verti- 
cal component.  The  horizontal  components  destroy 
each  other,  and  only  the  effect  of  the  vertical  compo- 
nents remains.  Hence  the  animals  are  forced,  as  a  re- 
sult of  their  positive  heliotropism,  to  crawl  upwards 
until  they  reach  the  tip  of  a  branch.  They  are  held 
there  by  the  light.  The  chemical  stimuli  which  are 
transmitted  to  the  animal  by  the  young  buds  produce 
the  eating  movements.  In  this  instinct,  which  is 
necessary  for  the  preservation  of  life,  we  have  an- 
other instance  of  simple  positive  heliotropism,  and  the 
central  nervous  system  plays  only  the  r6le  of  a  proto- 
plasmic connection  between  the  skin  and  contractile 
tissue,  which  in  plants  is  performed  just  as  success- 
fully by  undifferentiated  protoplasm. 

We  have  seen,  however,  that  these  same  caterpil- 
lars leave  the  tips  of  the  branches  as  soon  as  they 
have  eaten  and  crawl  downward.  Why  does  the 
light  not  hold  them  on  the  highest  point  permanently  ? 
My  experiments  showed  that  these  caterpillars  are 
only  positively  heliotropic  as  long  as  they  remain  un- 
fed ;  after  having  eaten  they  lose  their  positive  helio- 
tropism. This  is  not  the  only  instance  of  this  kind, 
for  I  have  found  a  series  of  facts  which  show  that 
chemical  changes  influence  the  irritability  of  the  ani- 
mal toward  light.  We  can  imagine  that  the  taking 
up  of  food  leads  to  the  destruction  of  the  substances 


I90  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

in  the  skin  of  the  animal  which  are  sensitive  to  Hght, 
upon  which  substances  the  heHotropism  depends,  or 
that  through  the  consumption  of  food  the  action  of 
these  substances  is  indirectly  prevented. 

6.  The  analysis  of  other  instincts,  for  instance,  the 
migratory  instinct  of  animals,  leads  to  the  same  result 
as  the  analysis  of  the  protective  instincts.  These  in- 
stincts are  not  functions  of  certain  localised  *'  centres," 
but  of  irritabilities  of  certain  peripheral  structures  and 
of  the  connection  of  the  same  with  the  muscles,  whereby 
the  central  nervous  system  only  serves  as  a  protoplas- 
mic connection.  It  would  naturally  be  more  inter- 
esting to  select  for  our  discussion  the  migrations  of 
birds,  but  it  is  difficult  to  make  laboratory  experi- 
ments on  this  subject,  and  without  laboratory  experi- 
ments we  cannot  easily  obtain  reliable  results.  For 
this  reason  I  have  made  use  of  another  class  of 
periodic  migrations,  namely,  the  periodic  depth-migra- 
tions of  pelagic  animals.  A  great  number  of  these 
animals  begin  a  vertical  upward  migration  toward  the 
surface  of  the  ocean  in  the  evening,  while  in  the 
morning  they  migrate  downwards.  It  is  a  remarkable 
fact  that  these  forms  never  go  below  a  depth  of  four 
hundred  metres  in  their  downward  migrations.  This 
fact  suggests  that  the  light  is  the  controlling  power 
in  these  depth-migrations.  Water  absorbs  the  light, 
and  the  thicker  the  layer  of  water  the  more  the  light 
is  absorbed.  It  has  been  found  that  at  a  depth  of 
four  hundred  metres  a  photographic  plate  is  no  longer 
affected.     My  investigations  show  that  the  movable 


THEORY  OF  INSTINCTS  191 

animals  living  at  the  surface  of  the  ocean  are  all  per- 
manently or  transitorily  positively  heliotropic  (and 
also  often  negatively  geotropic).  Those  among  them 
that  carry  out  the  daily  depth-migrations  described 
above  have  some  other  peculiarities  which  wo  can 
only  understand  if  we  go  somewhat  deeper  into  the 
theory  of  animal  heliotropism.  We  have  already 
mentioned  that  there  is  a  negative  as  well  as  a  posi- 
tive heliotropism  :  negatively  heliotropic  animals  bring 
their  median-plane  into  the  direction  of  the  rays  of 
light,  but  turn  their  aboral  pole  toward  the  source  of 
light.  The  difference  in  the  behaviour  of  negatively 
and  positively  heliotropic  animals  is  as  follows  :  If 
light  strikes  one  side  of  a  positively  heliotropic  animal, 
an  increase  takes  place  in  the  tension  of  those  mus- 
cles which  turn  the  head  to  the  source  of  light,  while 
in  the  negatively  heliotropic  animal  under  the  influ- 
ence of  one-sided  illumination  a  decrease  takes  place 
in  the  tension  of  the  same  muscles.  The  result  is 
that  the  negatively  heliotropic  animal  is  forced  to 
move  away  from  the  source  of  light.  Perhaps  still 
another  possibility  should  be  considered  here,  namely, 
that  the  light  aids  the  progressive  movement  when  it 
strikes  the  oral  end  of  a  positively  heliotropic  animal, 
while  it  inhibits  the  progressive  movement  when  it 
strikes  the  aboral  end.  The  opposite  may  be  true  of 
negatively  heliotropic  animals.  This  would  suggest 
a  further  analogy  between  heliotropism  and  galvano- 
tropism. 

Groom  and  I  performed  experiments  on  the  larvae 


192  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

of  Balanus  perforatus  which  were  known  to  make 
periodic  depth-migrations  (2).  As  one  of  our  results, 
we  found  that  these  animals  are  sometimes  negatively, 
sometimes  positively  heliotropic,  and  that  we  were 
able  to  make  them  positively  or  negatively  heliotropic 
at  desire.  By  weak  light,  especially  gaslight,  which 
contains  comparatively  few  of  the  heliotropically  effect- 
ive blue  rays,  they  became  and  remained  positively 
heliotropic,  while  in  strong  light  they  soon  became 
negatively  heliotropic.  This  circumstance  determines 
the  periodic  depth-migration  of  these  animals.  When 
they  are  near  the  surface  of  the  ocean  in  the  morning, 
the  strong  light  makes  them  negatively  heliotropic  and 
forces  them  to  go  downwards  vertically,  because  in 
the  open  sea  only  the  vertical  components  of  the  re- 
flected skylight  have  any  effect.  As  soon  as  they 
approach  a  depth  where  the  light  is  sufficiently  weak, 
they  become  positively  heliotropic.  They  must  then 
begin  to  migrate  upward  again,  but  cannot  reach  the 
surface,  because  they  soon  come  to  a  region  where  the 
light  is  so  strong  that  they  again  become  negatively 
heliotropic.  Hence  during  the  day  they  are  held  at  a 
certain  depth,  which  is,  however,  less  than  four  hun- 
dred metres.  But  as  soon  as  it  becomes  dark  and  the 
intensity  of  the  light  decreases  more  and  more,  they 
are  forced  to  rise  to  higher  regions  on  account  of  their 
positive  heliotropism,  until  during  the  night,  while  the 
intensity  of  the  light  is  weak,  they  are  held  at  the  sur- 
face of  the  water.  Toward  morning,  when  it  begins 
to  dawn,  they  again  become  negatively  heliotropic  and 


I 


THEORY  OF  INSTINCTS  193 

once  more  begin  their  downward  migration.  But  the 
pelagic  animals  also  show  another  depth-movement 
of  a  greater  period,  which  corresponds  more  nearly 
with  the  migration  of  birds  of  passage.  Chun  has 
found  that  in  the  Bay  of  Naples  during  summer  cer- 
tain forms  also  remain  at  a  greater  depth  during  the 
night,  never  coming  to  the  surface.  This  is  probably 
due  to  the  higher  temperature  which  the  surface  of 
the  water  has  in  summer.  I  have  found  that  certain 
animals,  for  instance,  the  larvae  of  Polygordius,  are 
positively  heliotropic  in  a  low  temperature,  while 
in  a  higher  temperature  they  become  negatively 
heliotropic  (4). 

I  have  also  mentioned  that  geotropism  also  plays  a 
part  in  these  depth-migrations.  The  same  circum- 
stances which  make  the  animals  negatively  helio- 
tropic also  make  them  positively  geotropic,  and  vice 
versa.  Thus  I  was  able  to  show  that  in  a  low  tem- 
perature the  larvae  of  Polygordius  are  also  negatively 
geotropic,  while  in  a  high  temperature  they  are  posi- 
tively geotropic  (4).  By  means  of  this  geotropism 
they  are  also  forced  in  the  dark  to  go  to  the  surface 
when  the  temperature  of  the  water  is  low.  It  is  also 
probable  that  in  many  forms  internal  conditions  simi- 
lar to  the  nyctitropic  phenomena  in  plants  are  in- 
fluential in  causing  periodic  depth-migrations.^  We 
thus  find  that  the  migratory  instinct,  as  far  as  it  is 

*  This  may  account  for  the  periodic  migrations  of  certain  animals  (Medusae) 
in  polar  regions.  In  such  animals,  changes  in  the  specific  gravity  may  take 
the  place  of  heliotropic  reactions. 

13 


194  COMPARATIVE  PHYSIOLOGY  OF   THE  BRAIN 

expressed  in  the  depth-migration  of  pelagic  animals,  is 
frequently  determined  by  the  presence  of  substances 
in  the  surfaces  of  the  animal  which  are  sensitive  to 
light.  These  substances,  however,  produce  different 
effects  according  to  the  intensity  of  the  light  or  of 
the  temperature  (or  perhaps  according  to  internal 
conditions).  They  are  further  determined  by  the  re- 
lations of  symmetry  of  the  animals.  The  central 
nervous  system  has  nothing  further  to  do  with  these 
phenomena  than  that  it  furnishes  the  protoplasmic 
connection  between  the  skin  and  muscles.  This  dis- 
agrees with  the  centre  theory  of  these  instincts,  but 
agrees  with  the  segmental  theory. 

7.  One  might  think  that  these  ideas  held  good  only 
for  Invertebrates.  Goltz  has,  however,  made  a  re- 
markable discovery  which  seems  to  confirm  the  opin- 
ion that  in  Vertebrates  the  conditions  are  practically 
the  same.  A  female  dog  that  has  given  birth  to  a 
young  one  bites  off  the  navel  cord,  licks  the  young,  is 
very  affectionate  towards  it,  and  allows  no  stranger  to 
touch  it.  These  motherly  instincts  are  inherited,  and 
there  is  no  doubt  that  with  the  act  of  giving  birth  and 
the  resulting  processes  in  the  sexual  organs  changes 
take  place  in  the  animal  which  make  these  instincts 
possible.  One  might  think,  especially  in  this  case,  of 
centres  in  the  central  nervous  system  which  are  stim- 
ulated directly  through  the  nerves  of  the  uterus.  Now 
Goltz  found  that  these  instincts  are  also  fully  devel- 
oped in  dogs  whose  spinal  cord  is  severed  so  far  up 
that  the  stimuli  from  the  uterus  cannot  reach  the 


I 


THEORY  OF  INSTINCTS  195 

brain  (6).  It  is  probable  that  certain  substances 
which  are  developed  during  the  pregnancy,  birth,  and 
lactation  influence  the  character  of  the  animal,  just 
as  certain  poisons,  for  instance,  alcohol,  tobacco,  or 
morphine,  influence  the  reactions  of  a  human  being. 
It  is  of  course  possible  that  the  sympathetic  plays  a 
part  here,  although  this  has  been  rendered  improbable 
through  the  more  recent  experiments  of  Goltz  and 
Ewald  and  of  Ribbert.^ 

8.  We  have  confined  our  attention  to  the  simplest 
instincts,  for  these  are  best  adapted  for  a  complete  an- 
alysis. Should  we  attempt  a  complete  enumeration 
and  discussion  of  instincts,  we  should  have  to  devote 
several  volumes  to  that  subject  alone.  We  should 
like  to  call  attention  to  the  conditions  which  are  re- 
sponsible for  the  fact  that  many  instincts  are  difficult 
to  analyse.  One  source  of  complication  lies  in  the 
fact  already  mentioned,  that  changes  in  the  condition 
of  the  blood,  for  example,  those  produced  by  metabol- 
ism, may  change  the  forms  of  irritability  and  reaction. 
The  young  caterpillar  of  Porthesia  is  only  heliotropic 
so  long  as  it  is  starving,  while  it  becomes  indifferent 
to  light  as  soon  as  it  is  fed.  In  plant-lice,  the  helio- 
tropic irritability  is  connected  with  the  growth  of 
wings.  The  wingless  forms  may  or  may  not  show 
positive  heliotropism ;  if  we  produce  wings  (by 
lowering  the  temperature  or  by  letting  the  plant  on 
which  it  lives  dry  out),  the  animal  becomes  energetic- 
ally positively  heliotropic.   In  ants  heliotropism  is  more 

*  See  next  chapter. 


196  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

intimately  connected  with  the  sexual  development.  I 
have  never  found  true  heliotropism  in  the  workers, 
while  the  sexually  mature  males  and  females  are  de- 
cidedly positively  heliotropic.  Wherever  these  tran- 
sitory changes  of  irritability  are  present,  it  requires 
experimental  work  to  succeed  in  the  analysis  of  the 
instinct. 

A  second  series  of  difficulties  arises  from  the  influ- 
ence of  associative  memory  in  many  cases  of  instincts. 
The  periodic  depth-migration  of  marine  animals  is  a 
simple  case  of  instinctive  migrations,  while  the  migra- 
tions of  birds  or  the  accomplishments  of  the  carrier- 
pigeon  seem  to  be  complicated  by  memory.  It  seems 
to  be  certain  that  the  carrier-pigeon  finds  its  way  back 
by  its  visual  memory  of  the  locality  from  which  it 
started.  In  the  same  way  the  migration  of  birds  may 
be  determined,  if  it  is  true  that  migrating  birds  return 
to  their  old  nest.  In  the  case  of  the  birds,  there  is 
present  in  addition  a  purely  inherited,  instinctive 
element  which  causes  restlessness  at  the  time  of 
migration.  This  restlessness  and,  perhaps  to  a  cer- 
tain extent,  the  direction  of  its  flight  are  susceptible 
of  a  purely  physiological  analysis.  The  element  of 
memory  complicates  many  instinctive  actions  of  wasps. 
I  have  had  a  chance  to  observe  solitary  wasps  and  am 
convinced  that  they  find  the  way  to  their  nest  by  means 
of  the  visual  memory  of  the  locality  where  it  is  situ- 
ated. The  same  is  apparently  true  of  bees  and  pos- 
sibly of  ants.     (See  Chapter  XV.) 

9.  The  analysis  of  instincts  from  a  purely  physio- 


THEORY  OF  INSTINCTS  197 

logical  point  of  view  will  ultimately  furnish  the  data 
for  a  scientific  ethics.  Human  happiness  is  based  up- 
on the  possibility  of  a  natural  and  harmonious  satis- 
faction of  the  instincts.^  One  of  the  most  important 
instincts  is  usually  not  even  recognised  as  such, 
namely,  the  instinct  of  workmanship.''^  Lawyers, 
criminologists,  and  philosophers  frequently  imagine 
that  only  want  makes  man  work.  This  is  an  errone- 
ous view.  We  are  instinctively  forced  to  be  active 
in  the  same  way  as  ants  or  bees.  The  instinct  of 
workmanship  would  be  the  greatest  source  of  happi- 
ness if  it  were  not  for  the  fact  that  our  present  social 
and  economic  organisation  allows  only  a  few  to  sat- 
isfy this  instinct.  Robert  Mayer  has  pointed  out  that 
any  successful  display  or  setting  free  of  energy  is  a 
source  of  pleasure  to  us.  This  is  the  reason  why  the 
satisfaction  of  the  instinct  of  workmanship  is  of  such 
importance  in  the  economy  of  life,  for  the  play  and 
learning  of  the  child,  as  well  as  for  the  scientific  or 
commercial  work  of  the  man. 

10.  We  have  finally  to  defend  our  physiological 
analysis  of  instincts  against  the  reproach  that  it  ignores 
the  theory  of  evolution.      In  other  words,  it  has  been 

'  It  is  rather  remarkable  that  we  should  still  be  under  the  influence  of  an 
ethics  which  considers  the  human  instincts  in  themselves  low  and  their  gratifi- 
cation vicious.  That  such  an  ethics  must  have  had  a  comforting  effect  upon 
the  Orientals,  whose  instincts  were  inhibited  or  warped  through  the  combined 
effects  of  an  enervating  climate,  despotism,  and  miserable  economic  conditions, 
is  intelligible,  and  it  is  perhaps  due  to  a  continuation  of  the  unsatisfactory  eco- 
nomic conditions  that  this  ethics  still  prevails  to  some  extent. 

^  I  take  this  name  from  Veblen's  book  on  The  Theory  of  the  Leisure  Class^ 
New  York,  1899. 


198  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

urged  against  us  that  instincts  should  be  explained 
historically  and  not  physiologically  or  causally.  It 
seems  to  me  that  living  organisms  are  machines  and 
that  their  reactions  can  only  be  explained  according 
to  the  same  principles  which  are  used  by  the  physicist. 
Our  ultimate  aim  in  the  analysis  of  instincts  is  to  find 
out  by  which  physical  and  chemical  properties  of  pro- 
toplasm they  are  determined.  Of  course  the  physicist 
finds  it  useful  to  illustrate  the  mechanism  of  compli- 
cated machines  by  the  comparison  with  simpler  or 
older  machines  of  the  same  kind.  We  have  made  use 
of  this  same  method  and  heuristic  principle  by  utilis- 
ing in  this  book  the  reactions  of  simpler  forms  for  the 
analysis  of  more  complicated  forms.  Even  if  we 
were  ill  possession  of  a  scientific  phylogeny  instead  of 
the  fairy  tales  that  go  by  that  name  at  present,  it 
would  not  relieve  us  of  the  task  of  explaining  the 
instincts  on  the  basis  of  the  physical  and  chemical 
qualities  of  protoplasm. 

II.  At  first  sight  it  may  seem  a  hopeless  task  to 
find  a  connection  between  the  instinctive  actions  of 
animals  and  the  properties  of  their  protoplasm.  And 
yet  the  task  is  not  so  great  if  we  choose  the  right 
method.  This  method,  in  my  opinion,  consists  in 
varying  the  instincts  of  an  animal  at  desire.  If  we 
succeed  in  this  we  are  able  to  find  out  how  the  physi- 
cal qualities  of  protoplasm  may  affect  the  instincts.  I 
have  tried  this  in  one  case.  A  number  of  marine  ani- 
mals (Copepods,  larvse  of  Polygordius)  which  go  away 
from  the  light  can  be  forced  to  go  to  the  light  in  two 


THEORY  OF  INSTINCTS  199 

ways,  first  by  lowering  the  temperature,  and  second, 
by  increasing  the  concentration  of  the  sea-water 
(whereby  the  cells  of  the  animals  lose  water).  This 
instinct  can  again  be  reversed  by  raising  the  tempera- 
ture or  by  lowering  the  concentration  of  the  sea- 
water.  Hence  these  instincts  must  depend  upon 
such  reversible  changes  in  the  material  of  the  proto- 
plasm as  can  be  brought  about  by  a  loss  of  water  or 
by  a  reduction  of  temperature.  What  these  changes 
are  can  only  be  determined  by  further  experiments. 
We  find  other  instances  where  decrease  in  tempera- 
ture has  the  same  physiological  effects  as  a  loss  of 
water.  Plant-lice  exist  in  wingless  and  in  winged 
forms.  We  can  at  any  time  cause  the  growth  of 
wings  in  the  wingless  forms  by  lowering  the  tempera- 
ture or  by  letting  the  plant  dry  out  (whereby  the 
amount  of  water  in  the  cells  of  plant-lice  is  reduced).^ 

Bibliography. 

1.  LoEB,  J.  Der  Heliotropismus  der  Thiere  und  seine  Ueber- 
einstimmung  mit  dem  Heliotropismus  der  Pflanzen.  Wiirzburg 
1890. 

2.  Groom  and  Loeb.  Der  Heliotropismus  der  Nauplien  von 
Balanus  perforatus  und  die  periodischen  Tiefenwanderungen  pelagis- 
cher  Thiere.     Biologisches  Centralblatt^  Bd.  x.,  1890. 

3.  Loeb,  J.  Ueber  den  Instinct  und  Willen  der  Thiere, 
P Auger's  ArchiVy  Bd.  xlvii.,  p.  407,  1890. 

'  I  have  found  repeatedly  that  by  the  same  conditions  by  which  phenomena  of 
growth  and  organisation  can  be  controlled  the  instincts  are  controlled  also. 
This  indicates  that  there  is  a  common  basis  for  both  classes  of  life  phenomena. 
This  common  basis  is  the  physical  and  chemical  character  of  the  mixture  of 
substances  which  we  call  protoplasm. 


200  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

4.  LoEB,  J.  Ueber  kunstliche  Umwandlung  positiv  heliotropis- 
cher  Thiere  in  negativ  heliotropische  und  umgekehrt.  Pfliiger's 
Archiv,  Bd.  liv.,  1893. 

5.  LoEB,  J.  On  Egg  Structure  and  the  Heredity  of  Instincts. 
The  Monist,  July,  1897. 

6.  GoLTZ,  F.  Ueber  den  Einfluss  des  Nervensystems  auf  die 
Vorgdnge  wdhrend  der  Schwangerschaft  und  des  Geburtsaktes. 
PflUger's  Archiv,  Bd.  ix.,  1874. 


CHAPTER  XIV 

THE  CENTRAL  NERVOUS  SYSTEM   AND 
HEREDITY 

I.  The  question  as  to  how  far  the  central  nervous 
system  comes  into  consideration  for  the  processes  of 
heredity  is  of  great  importance  in  educational  prob- 
lems. If  we  could  hope  that,  as  a  result  of  the  activ- 
ity of  a  generation,  its  descendants  would  be  born 
with  a  talent  for  this  special  activity,  there  would  be  a 
fertile  field  for  the  improvement  of  the  human  race. 
In  order  to  decide  this  question,  we  must  first  turn  our 
attention  to  those  peculiarities  which  we  know  to  be 
hereditary — namely,  the  form  of  the  body  and  the  in- 
stincts. The  analysis  of  the  instincts  given  in  the 
previous  chapter  places  us  in  a  position  to  answer  the 
question  as  to  how  they  can  be  transmitted  through 
the  ^^g.  All  hereditary  qualities  of  form,  instincts, 
and  reflexes  must  be  transmitted  through  the  sex- 
ual cells.  The  difficulty  that  appears  is  this  :  How 
can  the  sexual  cells,  which  only  represent  a  liquid 
mass  enclosed  in  solid  membranes,  be  the  bearers  of 
such  apparently  complicated  structures  as  the  forms 
that    originate    from   them  with    their  instincts  and 

20I 


202    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

reflexes  ?  Either  the  apparent  sImpHcity  of  the  struct- 
ure of  the  egg  is  only  an  illusion,  and  in  reality  the 
structure  of  the  ^gg  is  no  less  complicated  than  the 
full-grown  animal,  or  the  sum  of  the  elements  which 
we  call  the  form  and  instincts  of  the  full-grown  ani- 
mal is  only  the  resultant  of  a  few  simpler  elements 
which  can  readily  be  transmitted  through  the  ^gg 
without  its  possessing  a  complicated  structure.  The 
discussion  of  the  mechanics  of  instincts  in  the  last 
chapter  shows  the  latter  to  be  the  case.  Let  us  con- 
sider those  instincts  that  depend  on  heliotropic  reac- 
tions— for  instance,  the  flying  of  the  moth  into  the 
flame.  This  instinct  is  unequivocally  determined,  first, 
by  the  presence  of  a  substance  in  the  surface  of  the 
animal  which  is  sensitive  to  light,  and  second,  by  the 
symmetrical  structure  of  the  animal.  For  the  trans- 
mission of  a  substance  which  is  sensitive  to  light 
through  the  ^gg  no  complicated  mysterious  structure 
is  necessary.  Neither  is  a  complicated  structure 
necessary  for  the  ^gg  in  order  that  it  may  transmit 
the  symmetrical  relations  of  the  animal. 

For  the  inheritance  of  form  the  conditions  are  not 
very  different.  The  ^gg  is  not  the  bearer  of  the  form 
of  the  full-grown  animal,  but  of  certain  chemical  sub- 
stances, especially  of  ferments.  According  to  the 
stereochemical  configuration  of  the  latter,  the  products 
of  assimilation,  and  with  these  the  materials  of  the 
body,  turn  out  differently.  The  process  of  develop- 
ment is  not  only  a  morphological  but  a  chemical  dif- 
ferentiation, and  new  combinations  of  substances  are 


NERVOUS  SYSTEM  AND  HEREDITY         203 

continually  formed  from  the  original  raw  material. 
A  further  differentiation  of  the  form  may  be  and  often 
is  connected  with  every  metabolic  differentiation  of 
the  substance  of  the  body.  The  results  of  experi- 
mental morphology  harmonise  entirely  with  this  con- 
ception which  was  originated  by  Jaeger  and  Sachs, 
and  which  I  have  tried  to  develop  in  a  series  of 
articles.  I  will  only  mention  the  experiment  in  which 
the  ^^'g  of  the  sea-urchin  (Arbacia)  was  given  the 
form  of  a  double  sphere,  whereby  each  sphere  de- 
veloped into  a  complete  sea-urchin.  In  this  case  it 
makes  no  difference  whether  the  transformation  of 
the  sea-urchin  into  a  double  sphere  takes  place  in  the 
freshly  fertilised  ^gg  or  after  the  ^gg  has  already 
reached  the  16- or  32-cell  stage.  These  facts  can  only 
be  understood  if  we  think  of  the  ^gg  as  nothing  more 
than  the  bearer  of  certain  chemical  swhstdinc^s  and  not 
of  mysterious  morphological  structures  of  a  nature  as 
complicated  as  that  of  the  full-grown  animal ;  and  if 
we  regard  the  morphological  process  of  development 
only  as  a  result  or  accompanying  phenomenon  of 
corresponding  chemical  transformations  and  physical 
changes.  We  may  mention  further  in  this  connec- 
tion that  the  processes  of  heteromorphosis — that  is, 
the  transformation  or  substitution  of  one  organ  for 
a  morphologically  different  one  by  means  of  certain 
external  influences — force  us  to  the  same  view. 

2.  Tornier  has  developed  a  theory  of  the  inherit- 
ance of  acquired  characters  on  the  assumption  of  a 
new  role  of  the  central  nervous  system.     According 


204    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

to  this  theory,  every  change  that  takes  place  in  the 
body  is  said  to  be  accompanied  by  a  corresponding 
change  in  the  central  nervous  system.  The  changes 
in  the  central  nervous  system  are  then  said  to  bring 
about  a  corresponding  change  in  the  ^^g.  Thus,  ac- 
cording to  this  theory,  just  as  close  a  relation  must 
exist  between  the  central  nervous  system  and  the 
morphogenetic  processes  as  between  the  central  nerv- 
ous system  and  the  motor  and  sensory  functions. 
It  can  readily  be  shown,  however,  that  this  assumption 
of  Tornier  goes  much  too  far.  When  the  larva  of 
Amblystoma  transforms  itself  into  a  sexually  mature 
animal,  it  loses  the  gills  which  are  located  on  the  head 
and  the  tail-fins  that  are  on  the  tail.  Both  organs 
disappear  simultaneously.  In  a  series  of  Amblystoma 
larvae  I  severed  the  spinal  cord  in  the  vicinity  of  the 
shoulder-girdle.  The  parts  of  the  animal  before  and 
behind  the  place  of  division  are,  as  regards  motor  and 
sensory  functions,  like  two  separate  animals.  If  the 
morphogenetic  processes  were  as  closely  related  to 
the  central  nervous  system  as  the  sensory  and  motor 
functions  —  as  Tornier's  theory  demands  —  we  should 
have  expected  that  the  gills  and  tail-fins  would  no 
longer  be  absorbed  simultaneously,  but  at  different 
times,  just  as  in  two  different  animals.  Without  ex- 
ception, in  these  animals  with  severed  spinal  cord  the 
absorption  of  the  head-  and  tail-organs  occurred  simul- 
taneously (i).  In  some  of  the  animals  operated  upon, 
the  change  took  place  in  a  few  days  after  the  division, 
in  others  a  longer  interval  elapsed.     There  can  thus 


NERVOUS  SYSTEM  AND  HEREDITY         205 

be  no  doubt  that  the  connection  between  the  morpho- 
genetlc  functions  and  the  central  nervous  system  is 
much  more  sHght  than  between  this  organ  and  the 
sensory  and  motor  functions. 

I  am  incHned  to  believe  that  the  simultaneous  dis- 
appearance of  gills  and  tail-fins  is  due  to  some  change 
occurring  in  the  blood, — e.g.,  the  appearance  of  certain 
enzymes,  or  possibly  changes  in  the  number  of  red 
blood  corpuscles,  etc. 

It  has  been  urged  that  in  this  experiment  the  sympa- 
thetic system  transmitted  the  connection  between  the 
two  halves  of  the  animal.  The  sympathetic  has 
always  been  used  as  a  bridge  across  the  gulf  between 
preconceived  notions  and  facts.  I  am  pretty  certain 
that  at  least  in  a  number  of  my  Amblystomas  the  sym- 
pathetic was  cut.  But  as  I  did  not  make  sure  of  this 
I  will  not  urge  this  point.  But  I  may  at  least  point 
out  the  true  reliability  of  this  bridge.  It  had  been  a 
generally  accepted  belief  that  the  secretory  activity 
of  the  milk  glands  during  and  after  pregnancy  was 
caused  by  the  stimulation  of  the  nerve-endings  of  the 
uterus.  Goltz  severed  the  spinal  cord  in  the  pectoral 
region  of  a  female  dog  which  afterwards  became  preg- 
nant and  gave  birth  to  young  ones.  It  turned  out 
that  the  mammary  glands  in  front  and  behind  the  place 
of  the  section  began  to  secrete  milk  equally  well. 
Goltz  concluded  that  the  secretion  was  not  due  to  a 
nervous  influence.  As  was  to  be  expected,  those  who 
try  to  explain  everything  by  the  omnipotence  of  the 
central  nervous  system  at  once  pointed  out  that  the 


2o6    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

sympathetic  connected  the  two  halves  of  the  spinal 
cord  in  Goltz's  dog.  Recently  Ribbert  made  an  ex- 
periment which,  if  correct,  does  away  with  these 
mysterious  sympathetic  influences  (8).  He  trans- 
planted a  milk  gland  to  the  ear  of  a  guinea-pig.  The 
guinea-pig  became  pregnant  and  the  gland  on  the  ear 
began  to  secrete.  It  is  evident  that  a  change  in  the 
blood  or  lymph  must  be  responsible  for  the  secretion 
of  milk  glands  during  pregnancy,  possibly  the  appear- 
ance of  certain  enzymes. 

Schaper  has  added  an  experiment  that  speaks  for 
the  lack  of  dependence  of  the  morphogenetic  devel- 
opment on  the  central  nervous  system.  In  a  tadpole 
six  mm.  long  he  extirpated  the  brain  and  the  medulla 
oblongata.  When  the  animal  was  killed  seven  days 
later,  the  spinal  cord  seemed  to  have  vanished. 
Nevertheless  the  healing  of  the  wound,  growth,  and 
development  continued  during  the  seven  days  (2). 
In  face  of  the  fact  that  the  first  processes  of  de- 
velopment precede  the  formation  of  the  central  ner- 
vous system  in  every  animal,  these  results  need  not 
surprise  us.  They  suffice,  however,  to  convince  us 
that  the  processes  of  development  and  the  formation 
of  organs  are  less  closely  connected  with  the  central 
nervous  system  than  the  sensory  and  motor  processes. 
For  this  reason  we  cannot  well  decide  in  favour  of  the 
assumption  that  every  impression  on  the  central  nerv- 
ous system  must  impart  itself  to  the  ^^^,  with  which 
it  is,  moreover,  not  connected. 

3.   But  how  shall  we  make  the  fact  that  certain 


NERVOUS  SYSTEM  AND  HEREDITY         207 

mental  diseases  are  hereditary  harmonise  with  this 
view?  It  is,  perhaps,  not  impossible  that  those  men- 
tal diseases  that  are  hereditary  are,  in  reality,  chem- 
ical diseases  caused  by  poisons  that  are  formed  in  the 
body  just  as  special  substances,  for  instance,  alcohol, 
hashish,  and  other  intoxicating  substances,  produce 
temporary  mental  diseases  (3).  The  delirium  of  fever 
as  well  as  certain  other  mental  diseases  may  owe  their 
origin  to  poisons  which  are  formed  in  the  body.  It 
is  quite  possible  that  these  poisons  are  also  formed 
in  the  normal  body.  It  is  only  necessary  that  they  be 
formed  in  somewhat  larger  quantities  or  destroyed 
in  somewhat  smaller  quantities  in  the  body  of  the  in- 
sane than  in  the  normal  man.  It  is  further  not  at  all 
necessary  that  these  hypothetical  poisons  which  cause 
mental  diseases  be  formed  in  the  central  nervous  sys- 
tem. They  may  be  formed  in  any  organ  of  the  body. 
It  is  only  necessary  that  they  affect  the  central  nervous 
system  —  in  other  words,  that  they  be  nerve-poisons. 
Nothing  is  better  qualified  to  make  this  view  clear 
than  the  result  which  the  destruction  of  the  thyroid 
gland  has  on  the  mental  and  physical  development  of 
children.  We  know  that  in  case  of  degeneration  of  the 
thyroid  gland  the  growth  and  mental  development  of 
children  are  retarded.  Idiocy  may  result  from  the  de- 
struction of  the  thyroid  gland.  It  has  been  found 
that  an  improvement  or  even  a  cure  can  be  attained 
by  feeding  patients  afflicted  with  this  trouble  with 
the  thyroid  substance  of  animals.  Baumann  found 
that  the  thyroid  gland  contains  an  element  which  is 


2o8    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

contained  In  no  other  organ  of  the  body,  namely,  Io- 
dine. It  Is  thus  conceivable  that  hereditary  mental 
diseases  are  chemical  diseases.  The  germ-cells  may 
in  these  diseases  also  be  influenced  by  the  poisons 
circulating  In  the  blood. 

4.  If  we  thus  deny  the  immediate  Influence  of  the 
central  nervous  system  on  the  germ,  and  assume  a 
chemical  theory  of  heredity,  it  might  still  be  possible 
that  the  central  nervous  system  could  influence  hered- 
ity indirectly,  in  so  far  as  it  can  affect  the  chemical 
processes  of  the  body.  As  illustrations  of  a  chemical 
effect  of  the  nerves,  the  fact  is  mentioned  that  stimu- 
lation of  the  nerves  of  certain  glands  produces  a  secre- 
tion. Mathews  has  shown,  however,  that  in  cases 
where  stimulation  of  the  sympathetic  produces  a  secre- 
tion, the  glands  contain  muscular  fibres  which  contract 
when  stimulated,  and  in  this  way  press  a  liquid  out  of 
the  ducts  (4).  (Conditions  seem  to  be  different  in  the 
case  of  the  secretion  produced  by  stimulation  of  the 
chorda,  but  it  is  also  possible  that  in  this  case  the  secre- 
tion is  only  an  indirect  effect  of  the  stimulation  caused 
by  changes  In  the  circulation.)  There  are  other 
cases  of  an  apparent  chemical  effect  of  the  nerves. 
The  fact  that  herpes  zoster  follows  the  nerves  has 
led  many  to  assume  that  this  disease  Is  caused  by  a 
trophical  influence  of  the  nerves.  But  we  know  that 
in  the  case  of  rabies  the  micro-organism  or  the  poison 
creeps  along  the  nerves.  Goltz  has  found  that  ulcer- 
ations and  suppurations  occur  on  the  skin  behind  the 
cut  after  division  of  the  spinal  cord,  which  are  so  sym- 


NERVOUS  SYSTEM  AND  HEREDITY         209 

metrical  that  it  is  impossible  to  attribute  them  solely 
to  external  injuries.  They  occur  only  during  the  first 
weeks  after  the  operation,  disappearing  later  on  (5). 
It  is  conceivable  that  the  cause  of  these  phenomena  is 
to  be  sought  in  abnormal  chemical  processes  which 
are  perhaps  caused  by  the  vasomotor  nerves  in  so  far 
as  disturbances  in  the  supply  of  oxygen,  etc.,  are  de- 
termined by  them.  These  disturbances  occasionally 
fail  to  appear.  Physicians  are  familiar  with  these 
phenomena  of  bed-sores  which  ensue  after  lesion  of 
the  spinal  cord.  One  fact  that  Goltz  and  Ewald  found 
is  especially  interesting  for  the  theory  of  these  pro- 
cesses. When  they  severed  the  spinal  cord  of  animals, 
these  phenomena  of  ulceration  of  the  skin  were  very 
pronounced.  But  if  they  afterward  operated  on  the 
spinal  cord  behind  the  cut,  the  disturbances  were  much 
less  severe  or  failed  to  appear.  Thus  the  separation 
of  a  part  of  the  spinal  cord  from  the  brain  is  accom- 
panied by  more  serious  consequences  than  the  sub- 
sequent destruction  of  the  spinal  cord  itself  (5). 

An  inflammation  of  the  cornea  occurs  generally 
after  the  division  of  the  trigeminus  of  the  same  side. 
This  inflammation  is  naturally  caused  by  bacteria,  but 
the  fact  that  these  bacteria  affect  the  cornea  whose 
sensory  nerve  is  severed  might  have  two  causes : 
either  the  animal  on  account  of  the  lack  of  sensibility 
might  not  notice  the  foreign  bodies  (dust,  etc.)  that 
get  into  the  eye  and  cause  a  wound,  or  as  a  result  of 
the  division  of  the  nerve  changes  take  place  in  the 
cornea  which  render  it  more  susceptible  to  inflam- 


2IO    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

matlon.  The  latter  might  be  the  case  if  Gaule's 
statement  is  correct,  namely,  that  histological  changes 
can  be  shown  in  the  cornea  ten  minutes  after 
the  division  of  the  trigeminus  (6,  7).  In  this 
case  it  can  only  be  that  the  power  of  resistance 
or,  more  accurately  speaking,  the  chemical  nature 
of  the  tissue  is  changed  as  a  result  of  the  lesion 
of  the  nerve.  If  this  be  true,  it  does  not  force 
us  to  the  assumption  of  specific  trophic  nerves  ;  if 
it  is  true  that  the  influence  of  every  nervous  im- 
pulse on  the  affected  tissue  is  chemical,  all  nerves  are 
in  one  sense  trophic,  and  it  would  be  quite  erroneous 
to  maintain  that  certain  nerves  serve  trophic  func- 
tions exclusively  while  others  are  sensory  and  motor. 
There  are  no  specifically  trophic  nerves,  but  it  is  pos- 
sible that  many  nerves  produce  indirectly  (for  instance, 
through  disturbances  of  the  circulation  and  limitation 
of  the  supply  of  oxygen)  such  extensive  chemical 
changes  that  morphological  changes  of  the  tissue 
ensue. 

If  this  is  in  reality  the  case,  a  possibility  still  exists 
that  the  central  nervous  system  also  affects  the  sex- 
ual cells  indirectly,  in  so  far  as  disturbances  of  circu- 
lation and  hence  chemical  changes  are  produced,  which 
may  modify  the  sexual  cells  contained  in  the  testes 
and  ovaries  chemically.  Thus  there  might  be  a  very 
remote  chance  that  brain-activity  of  one  generation 
might  lead  to  the  formation  of  chemical  substances 
which  affect  the  sexual  cells.  It  is  difficult  to  under- 
stand, however,  what  should  cause  these  sexual  cells 


NERVOUS  SYSTEM  AND  HEREDITY         211 

to  produce  descendants  with  greater  intellect.  The 
intellect  is  not  proportional  to  chemical  changes,  like 
muscular  activity.  In  the  brain  of  an  idiot  and  of  a 
genius  the  same  chemical  changes  may  occur.  The 
difference  between  the  two,  however,  is  that  the  idiot 
fails  to  notice  valuable  associations  of  ideas  while  the 
brain  of  the  genius  retains  them.  We  arrive  thus  at 
the  conclusion  that  a  transmission  of  hereditary  char- 
acteristics through  the  ^^g  is  only  possible  in  the 
form  of  specific  chemical  substances,  and  that  the 
central  nervous  system  could  only  influence  heredity, 
if  it  could  bring  about  the  formation  of  special  sub- 
stances in  the  ^g^  (by  influencing  metabolism).  It 
would,  of  course,  first  have  to  be  proved  that  the  cen- 
tral nervous  system  has  such  an  influence  upon  the 
sexual  cells,  and  this  is  extremely  doubtful.  For  this 
reason  we  should  not  be  justified  in  maintaining  that 
the  activity  of  a  generation  can  produce  an  heredi- 
tary increase  of  the  ability  and  tendencies  in  the  same 
direction.  Herbert  Spencer  gives  as  a  proof  of  this  last 
possibility  the  fact  that  the  circles  of  touch  in  the  tip 
of  our  tongue  are  the  smallest.  He  believes  that 
this  is  due  to  the  fact  that  from  time  immemorial  man 
had  the  tendency  to  examine  the  spaces  between  the 
teeth  with  the  tongue,  and  this  is  supposed  to  have 
caused  an  hereditary  increase  in  the  nerve-endings  of 
the  tongue.  Spencer  overlooks  the  fact  that  in  the  tip 
of  the  nose  the  circles  of  touch  are  also  a  comparative 
minimum,  and  it  is  certain  that  this  organ  has  not 
been  used  for  such  a  purpose  since  time  immemorial. 


212    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

It  is  more  probable  that  the  relative  number  of  the 
nerve-endings  or,  more  correctly  speaking,  the  rela- 
tive size  of  the  circles  of  touch  in  the  tip  of  the 
tongue  and  the  tip  of  the  nose  is  determined  by  the 
relatively  small  radius  of  curvature  or  the  minimal 
areal  growth  of  these  tips. 

Bibliography. 

1.  LoEB,  J.  Hat  das  Central nervensy stem  einen  Einfluss  auf 
die  Vorgdnge  der  Larvenmetamorphosel  Archiv  fiir  Entwickelungs- 
mechanik,  Bd.  iv.,  1896. 

2.  ScHAPER,  A.  Experimental  Studies  on  the  Influence  of  the 
Central  Nervous  System  upon  the  Development  of  the  Embryo. 
Journal  of  the  Boston  Soc.  of  Medical  Science^  Jan.,  1898. 

3.  Meyer,  Adolf.  A  Short  Sketch  of  the  Problems  of  Psy- 
chiatry.    Am.  Jour,  of  Insanity,  vol.  liii.,  1897. 

4.  Mathews,  A.  The  Physiology  of  Secretion.  Annals  N. 
Y.  Acad,  of  Science,  vol.  xi.,  No.  14,  1898. 

5.  GoLTZ  and  Ewald.  P>er  Hund  mit  verkiirztem  Riicken- 
mark.     Pflilger's  Arch,,  Bd.  Ixiii.,  1896. 

6.  Gaule,  J.  Der  Einfluss  des  Trigeminus  auf  die  Hornhaut. 
Physiologisches  Centralblatt,  Bd.  v.,  1891. 

7.  Gaule,  J.  Wie  beherrscht  der  Trigeminus  die  Erndhrung 
der  Hornhaut.     Physiologisches  Centralblatt,  Bd.  vi.,  1892. 

8.  RiBBERT,  H.  Ueber  Transplantation  von  Ovarium,  Hoden 
und  Mamma.     Arch.  f.  Entwickelungsmechanik,  vol.  vii.,  1898. 


CHAPTER  XV 

THE  DISTRIBUTION  OF  ASSOCIATIVE  MEMORY 
IN  THE  ANIMAL  KINGDOM 

I.  The  most  important  problem  in  the  physiology 
of  the  central  nervous  system  is  the  analysis  of  the 
mechanisms  which  give  rise  to  the  so-called  psychic 
phenomena.  The  latter  appear,  invariably,  as  a  func- 
tion of  an  elementary  process,  namely,  the  activity  of 
the  associative  memory.  By  associative  memory  I 
mean  the  two  following  peculiarities  of  our  central 
nervous  system  :  First,  that  processes  which  occur 
there  leave  an  impression  or  trace  by  which  they  can 
be  reproduced  even  under  different  circumstances 
than  those  under  which  they  originated.  This  pecu- 
liarity can  be  imitated  by  machines  like  the  phono- 
graph. Of  course,  we  have  no  right  to  assume  that 
the  traces  of  processes  in  the  central  nervous  system 
are  analogous  to  those  in  the  phonograph.  The  sec- 
ond peculiarity  is,  that  two  processes  which  occur 
simultaneously  or  in  quick  succession  will  leave  traces 
which  fuse  together,  so  that  if  later  one  of  the  pro- 
cesses is  repeated,  the  other  will  necessarily  be  re- 
peated also.     The  odour  of  a  rose  will  at  the  same 

213 


214    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

time  reproduce  its  visual  image  in  our  memory,  or, 
even  more  than  that,  it  will  reproduce  the  recollection 
of  scenes  or  persons  who  were  present  when  the  same 
odour  made  its  first  strong  impression  on  us.  By 
associative  memory  we  mean,  therefore,  that  mechan- 
ism by  means  of  which  a  stimulus  produces  not  only 
the  effects  which  correspond  to  its  nature  and  the 
specific  structure  of  the  stimulated  organ,  but  which 
produces,  in  addition,  such  effects  of  other  causes  as 
at  some  former  time  may  have  attacked  the  organism 
almost  or  quite  simultaneously  with  the  given  stimu- 
lus (2).  The  chief  problem  of  the  physiology  of  the 
brain  is,  then,  evidently  this  :  What  is  the  physical 
character  of  the  mechanism  of  associative  memory  ? 
As  we  said  in  the  first  chapter,  the  answer  to  this 
question  will  probably  be  found  in  the  field  of  physi- 
cal chemistry. 

I  think  it  can  be  shown  that  what  the  metaphys- 
ician calls  consciousness  are  phenomena  determined 
by  the  mechanism  of  associative  memory.  Mach  has 
pointed  out  that  the  consciousness  of  self  or  the  ego 
is  simply  a  phrase  for  the  fact  that  certain  constitu- 
ents of  memory  are  constantly  or  more  frequently 
produced  than  others  (i,  11).  The  complex  of 
these  elements  of  memory  is  the  "  ego  "  or  the  **  soul," 
or  the  personality  of  the  metaphysicians.  To  a  cer- 
tain extent  we  are  able  to  enumerate  these  con- 
stituents. They  are  the  visual  image  of  the  body  so 
far  as  it  lies  in  the  field  of  vision,  certain  sensations 
of   touch   which   are   repeated  very  frequently,  the 


DISTRIBUTION  OF  MEMORY  215 

sound  of  our  own  voice,  certain  interests  and  cares,  a 
certain  feeling  of  comfort  or  discomfort  according  to 
temperament  or  state  of  health,  etc.  (i,  11). 

An  inventory  of  all  the  memory-constituents  of  the 
ego-complex  of  different  persons  would  show  that  the 
consciousness  of  self  is  not  a  definite  unit,  but,  as 
Mach  maintains,  merely  an  artificial  separation  of 
those  constituents  of  memory  which  occur  most  fre- 
quently in  our  perceptions.  These  will  necessarily 
be  subject  to  considerable  variation  in  the  same  per- 
son in  the  different  periods  of  life. 

If  we  speak  of  loss  or  an  interruption  of  conscious- 
ness, we  mean  a  loss  or  an  interruption  of  the  activity 
of  associative  memory.  If  a  faint  is  caused  directly 
by  lack  of  oxygen  or  indirectly  by  a  disturbance  in  the 
circulatory  system,  the  activity  of  associative  memory 
ceases.  This  was  proved  by  Speck's  experiments  on 
the  effects  of  a  low  pressure  of  oxygen.  When  he 
breathed  air  with  less  than  eight  per  cent,  of  oxygen, 
he  soon  fainted.  In  these  experiments,  he  had  to 
count  the  number  of  respirations.  Before  he  fainted, 
he  became  confused  in  his  counting  and  forgot  what 
happened.  When  this  disturbance  in  counting  began 
to  appear,  he  knew  it  was  time  to  discontinue  the  ex- 
periment. When  a  loss  of  consciousness  is  produced 
by  narcotics  or  anaesthetics,  we  have  again  to  deal 
with  an  interruption  in  the  activity  of  the  associative 
memory.     It  is  the  same  in  the  case  of  a  deep  sleep. 

The  metaphysician  speaks  of  conscious  sensations 
and  conscious  will.     That  the  will  is  only  a  function 


2i6    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

of  the  mechanism  of  the  associative  memory  can  be 
proved.  We  speak  of  conscious  volition  if  an  idea 
of  the  resulting  final  complex  of  sensations  is  present 
before  the  movements  causing  it  have  taken  place  or 
have  ceased.  In  volition  three  processes  occur.  The 
one  is  an  innervation  of  some  kind  which  may  be 
caused  directly  or  indirectly  by  an  external  stimulus. 
This  process  of  innervation  produces  two  kinds  of 
effects.  The  one  effect  is  the  activity  of  the  associa- 
tive memory  which  produces  the  sensations  that  in 
former  cases  accompanied  or  followed  the  same  inner- 
vation. The  second  effect  is  a  coordinated  muscular 
activity.  It  happens  that  in  such  cases  the  reaction- 
time  for  the  memory-effect  of  the  innervation  is 
shorter  than  the  time  for  the  muscular  effect.  When 
some  internal  process  causes  us  to  open  the  window, 
the  activity  of  the  associative  memory  produces  the 
idea  of  sensations  which  will  follow  or  accompany 
the  opening  of  the  window  sooner  than  the  act  of 
opening  really  occurs.  As  we  do  not  realise  this 
any  more  than  we  realise  the  inverted  character  of 
the  retina-image,  we  consider  the  memory-effect  of  the 
innervation  as  the  cause  of  the  muscular  effect.  The 
common  cause  of  both  effects,  the  innervating  pro- 
cess, escapes  our  immediate  observation  as  our  senses 
do  not  perceive  it.  The  will  of  the  metaphysicians 
is  then  clearly  the  outcome  of  an  illusion  due  to  the 
necessary  incompleteness  of  self-observation.  Our 
conception  of  will  harmonises  with  Miinsterberg's 
and  James's  views  on  this  subject  (6,   12).     I  think 


DISTRIBUTION  OF  MEMORY  217 

that  we  are  justified  in  substituting  the  term  activity 
of  associative  memory  for  the  phrase  consciousness 
used  by  the  metaphysicians. 

2.  We  have  spoken  of  associative  memory  because 
the  word  memory  is  often  appHed  in  quite  a  different 
sense  scientifically,  namely,  to  signify  any  after-effect 
of  external  circumstances.  For  instance,  the  term 
memory  has  been  used  to  account  for  the  fact  that  a 
plant  which  had  been  cultivated  in  the  tropics  will 
often  not  endure  low  temperatures  so  well  as  a  plant 
of  the  same  species  which  was  raised  in  the  north.  It 
is  true  in  this  case  that  preceding  conditions  influence 
the  ability  of  the  plant  to  react,  but  the  process  differs 
from  the  one  which  we  have  called  associative  memory 
in  the  lack  of  associative  processes.  No  definite  stim- 
ulus produces  in  a  plant,  in  addition  to  its  own  effects, 
those  of  another  entirely  different  stimulus  which  at 
some  former  time  occurred  simultaneously  with  the 
given  stimulus.  It  is  probable  that  the  tropical  plant 
is  somewhat  different  chemically  from  the  plant  raised 
in  the  north.  This  would  account  for  its  smaller 
power  of  resistance.  Further  illustrations  of  a  differ- 
ent use  of  the  word  memory  can  easily  be  given. 

Many  moths  sleep  during  the  day  and  wake  in  the 
evening  when  it  becomes  dark.  If  kept  for  days  in 
a  dark  room,  they  will  continue  at  first  to  do  the  same 
thing.  The  same  is  true  of  certain  plants.  One 
might  also  say  in  this  case  that  the  moth  or  the  plant 
"  remembers  "  the  difference  between  day  and  night. 
It  is  probable,  however,  that  internal  changes  take 


2i8    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

place  in  the  organism,  corresponding  to  the  periodic 
change  of  day  and  night,  and  that  these  changes  con- 
tinue for  a  time  in  the  same  periodicity,  when  the  ani- 
mal is  kept  in  the  dark. 

3.  We  will  then  consider  the  extent  of  associative 
memory  in  the  animal  kingdom  instead  of  the  extent 
of  consciousness  among  animals.  How  can  we  deter- 
mine whether  an  animal  possesses  the  mechanism 
necessary  for  associative  memory  ?  The  criteria  for  the 
existence  of  associative  memory  must  form  the  basis 
of  a  future  comparative  psychology.  It  will  require 
more  observations  than  we  have  made  at  present  to 
give  absolutely  unequivocal  criteria.  For  the  present, 
we  can  say  that  if  an  animal  can  learn,  that  is,  if  it 
can  be  trained  to  react  in  a  desired  way  upon  certain 
stimuli  (signs),  it  must  possess  associative  memory. 
The  only  fault  with  this  criterion  lies  in  the  fact  that 
an  animal  may  be  able  to  remember  (and  to  associate) 
and  yet  may  not  yield  to  our  attempts  to  train  it.  In 
this  case  other  experiments  must  be  substituted  which 
will  prove  that  the  animal  does  associate  or  remember. 

We  may  conclude  that  associative  memory  is  pre- 
sent when  an  animal  responds  upon  hearing  its  name 
called,  or  when  it  can  be  trained  upon  hearing  a 
certain  sound  to  go  to  the  place  where  it  is  usually 
fed.  The  optical  stimulus  of  the  place  where  the 
food  is  to  be  found  and  the  sensations  of  hunger  and 
satiety  are  not  qualitatively  the  same,  but  they  occur 
simultaneously  in  the  animal.  The  fusion  or  growing 
together  of  heterogeneous  but  by  chance  simultaneous 


k 


DISTRIBUTION  OF  MEMORY  219 

processes  is  a  sure  criterion  for  the  existence  of  as- 
sociative memory  (2). 

Associative  memory  probably  exists  in  most  mam- 
mals. The  dog  which  comes  when  its  name  is  called, 
which  runs  away  from  the  whip,  which  welcomes  its 
master  joyfully,  has  associative  memory.  In  birds,  it 
is  likewise  present.  The  parrot  learns  to  talk  ;  the 
dove  finds  its  way  home.  In  lower  Vertebrates,  mem- 
ory is  also  occasionally  found.  Tree-frogs,  for  ex- 
ample, can  be  trained,  upon  hearing  a  sound,  to  go  to 
a  certain  place  for  food.  In  other  frogs,  Rana  escu- 
lenta,  for  instance,  no  reaction  is  as  yet  known  which 
proves  the  existence  of  associative  memory.  Some 
fishes  evidently  possess  memory  ;  in  sharks,  however, 
its  existence  is  doubtful.  With  regard  to  the  Inver- 
tebrates, the  question  is  difificult  to  determine.  The 
statements  of  enthusiasts  who  discover  consciousness 
and  resemblance  to  man  on  every  side  should  not  be 
too  readily  accepted. 

4.  In  my  experiments  on  the  tropismsof  animals,  it 
became  clear  to  me  how  easy  it  is  for  an  observer 
who  is  inclined  to  think  anthropomorphically  to  re- 
gard machine-like  effects  of  external  stimuli  on  lower 
animals  as  the  expression  of  intelligence.  He  needs 
only  to  neglect  the  analysis  of  the  external  stimuli.  I 
have  protested  against  the  anthropomorphisms  of 
Romanes,  Eimer,  Preyer,  and  others  in  a  series  of  ar- 
ticles (2,  3).  Bethe  has  recently  published  a  paper  on 
the  psychic  qualities  of  ants  and  bees  in  which  he 
took  special  pains  not  to  fall  into  the  gross  anthropo- 


220    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

morphisms  which  have  characterised  this  field  here- 
tofore (4).  But  I  am  afraid  that  he  went  too  far 
and  that  he  overlooked  the  fact  that  bees  and  ants 
possess  associative  memory.  Bethe  assumes  associa- 
tive memory  as  the  criterion  for  the  existence  of  con- 
sciousness, as  I  had  done  before.  (He  has  evidently 
overlooked,  or  at  least  does  not  mention,  my  work  on 
this  subject.)  According  to  him:  '*  An  animal  that 
is  able  to  do  the  same  things  the  first  day  of  its  exist- 
ence which  it  can  do  at  the  end  of  its  life,  that  learns 
nothing,  that  always  reacts  in  the  same  way  upon 
the  same  stimulus,  possesses  no  consciousness."  This 
statement  is  not  sufficient.  It  is  possible  that  an  ani- 
mal at  birth,  or  just  after  hatching,  may  not  be  fully 
developed.  In  this  case  it  may  be  able  later  to  per- 
form actions  which  would  have  been  impossible 
on  the  first  day,  without  possessing  associative  mem- 
ory. Yet  according  to  Bethe's  definition  such  actions 
would  indicate  associative  memory. 

It  is  a  well-known  fact  that  if  an  ant  be  removed 
from  a  nest  and  afterwards  put  back  it  will  not  be 
attacked,  while  almost  invariably  an  ant  belonging  to 
another  nest  will  be  attacked.  It  has  been  customary 
to  use  the  words  memory,  enmity,  friendship,  in  de- 
scribing this  fact.  Now  Bethe  made  the  following 
experiment.  An  ant  was  placed  in  the  liquids  (blood 
and  lymph)  squeezed  out  from  the  bodies  of  nest 
companions  and  was  then  put  back  into  its  nest ;  it 
was  not  attacked.  It  was  then  put  in  the  juice  taken 
from  the  inmates  of  a  *'  hostile  "  nest  and  was  at  once 


I 


DISTRIB  UTION  OF  MEM  OR  Y  221 

attacked  and  killed.  Hence  chemical  stimuli  of 
certain  volatile  substances  will  excite  the  ants.  In 
this  case  we  do  not  need  to  assume  intelligence  any 
more  than  we  do  in  the  case  of  the  tentacles  of  Ac- 
tinians  which,  as  we  have  seen,  will  immediately  carry 
a  piece  of  filter  paper  soaked  in  meat-juice  to  the  mouth 
while  they  ignore  a  piece  of  paper  soaked  in  sea-water. 
The  assumption  of  machine-like  irritable  structures  is 
quite  sufficient  here  to  explain  the  reaction.  Mem- 
ory is  quite  unnecessary.  Possibly  the  behaviour  of 
the  ant  may  be  explained  in  the  same  way.  Bethe 
was  able  to  prove  by  special  experiments  that  these 
reactions  of  ants  are  not  learned  by  experience, 
but 'are  inherited.  The  "knowing  "of  *' friend  and 
foe  "  among  ants  is  thus  reduced  to  different  reactions, 
depending  upon  the  nature  of  the  chemical  stimulus 
and  in  no  way  depending  upon  memory. 

Memory  and  intellect  are  supposed  to  be  responsible 
for  the  fact  that  an  ant  is  able  to  find  its  way  back  to 
the  nest  and  that  when  "  foragers  "  have  discovered 
honey  or  sugar  the  other  ants  of  the  nest  soon  go  to 
it  in  great  numbers.  The  ability  to  communicate  in- 
formation was  assumed  in  this  case.  Bethe,  however, 
was  able  to  determine  by  means  of  ingenious  experi- 
ments that  an  ant,  when  taking  a  new  direction  from 
the  nest  for  the  first  time,  always  returns  by  the  same 
path.  This  shows  that  some  trace  must  be  left  be- 
hind which  serves  as  a  guide  back  to  the  nest.  If 
the  ant  returning  by  this  path  bear  no  spoils,  Bethe 
found  that  no  other  ants  try  this  direction.     But  if  it 


222    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

bring  back  honey  or  sugar,  other  ants  are  sure  to  try 
the  path.  Hence  something  of  the  substances  carried 
over  this  path  by  the  ants  must  remain  on  the  path. 
These  substances  must  be  strong  enough  to  affect  the 
ants  chemically.  I  can  prove  by  the  following  obser- 
vation, which  must  surely  have  been  made  before  me 
by  many  breeders  of  butterflies,  that  Bethe  is  justified 
in  the  assumption  that  insects  are  affected  by  ex- 
tremely weak  chemical  stimuli.  I  placed  a  female 
butterfly  of  a  certain  species  in  a  cigar-box,  and  closed 
the  box.  The  box  was  then  suspended  half  way  be- 
tween the  ceiling  and  floor  of  the  room  and  then  the 
window  was  opened.  At  first  no  butterfly  of  this 
species  was  visible  far  or  near.  I  n  less  than  half  an  hour 
a  male  butterfly  of  the  same  species  appeared  on  the 
street.  When  it  reached  the  height  of  the  window, 
its  flight  was  retarded  and  it  came  gradually  toward 
the  window.  It  flew  into  the  room  and  soon  up  to 
the  cigar-box,  upon  which  it  perched.  During  the 
afternoon,  two  other  males  of  the  same  species  came 
to  the  box.  Thus  we  see  that  butterflies  and  certainly 
many  other  insects  possess  a  delicacy  of  chemical 
irritability  which,  if  possible,  is  finer  than  that  of  the 
best  blood-hound.  Plateau  maintains  that  insects  are 
attracted  to  the  flowers  by  the  odour  rather  than  by  the 
colour  and  marking.  The  dioptric  apparatus  of  insects 
is  very  inferior  to  that  of  the  human  eye,  while  their 
chemical  irritability  is  much  superior  to  that  of  our 
olfactory  epithelium.  I  believe  that  both  odour  and 
colour  may  influence  insects. 


DISTRIBUTION  OF  MEMORY  223 

One  of  the  most  remarkable  conclusions  of  Bethe 
is  the  assumption  that  the  roads  of  the  ants  have  two 
paths  which  differ  chemically  from  each  other,  one 
leading  from  and  one  toward  the  nest.  Bethe  tried 
to  prove  this  by  experiments  that  had  been  undertaken 
before  by  Lubbock,  who  obtained  no  definite  results. 
Bethe  arranged  a  broad  ant-street  so  that  it  led  over 
a  turn-bridge.  He  revolved  this  bridge  180°,  when 
the  ants  were  passing  to  and  from  the  nest,  and  found 
that  it  was  impossible  for  the  two  armies  to  continue 
on  their  way.  He  again  turned  the  bridge  180°  so 
that  the  tracks  had  the  original  orientation.  The 
ants  continued  in  the  direction  they  were  pursuing 
when  disturbed.  An  observation  made  by  Forel  also 
agrees  with  this :  "  An  ant  that  is  picked  up  from 
the  path  while  moving  and  then  put  down  again  is  al- 
most sure  to  take  the  same  direction,  no  matter  what 
orientation  is  given  to  its  body."  This,  however, 
only  holds  good  for  a  street  which  is  often  travelled. 
A  weak  track  which  leads  in  one  direction  is  qualified 
to  lead  in  the  opposite  direction,  as  is  shown  by  the 
fact  that  an  ant  which  has  found  a  new  supply  returns 
to  the  nest  the  same  way  that  it  came.  It  is  evidently 
the  load  and  lack  of  load  which  determine  which  path 
the  ant  will  take  (that  is,  to  or  from  the  nest).  The 
load  causes  the  ant  to  go  to  the  nest  reflexly  ;  the  lack 
of  a  load  causes  it  to  go  from  the  nest.  Bethe  comes 
to  the  conclusion  that  the  reactions  of  ants,  which 
have  always  been  considered  psychic  phenomena,  are 
merely  reflex  processes  comparable  to  the  tropisms. 


224  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

5.  Although  I  heartily  sympathise  with  Bethe's  re- 
action against  the  anthropomorphic  conception  of 
animal  instincts,  I  yet  believe  that  he  is  mistaken  in 
denying  the  existence  of  associative  memory  in  ants 
or  bees.  The  fact  that  bees  find  their  way  home 
through  the  air  cannot  depend  upon  any  trace  left  in 
their  path.  It  can  only  depend  upon  memory  and,  as 
I  believe,  upon  visual  memory.  If  the  bee-hive  be 
removed  while  the  bees  have  swarmed  out,  they  will 
return  to  and  gather  at  the  spot  where  the  entrance 
to  the  hive  used  to  be.  Bethe  is  not  willing  to  admit 
that  this  indicates  the  existence  of  a  visual  image  of 
memory  of  the  locality  of  the  nest,  professing  to  con- 
sider it  possible  that  unknown  forces  guide  the  bee 
reflexly. 

I  have  recently  had  a  chance  to  observe  the  activity 
of  solitary  wasps  and  have  come  to  the  conclusion 
that  these  animals  are  guided  back  to  their  nest  by 
their  memory. 

My  observations  were  made  on  Ammophila,  a  spe- 
cies of  wasps,  whose  habits  have  been  carefully  stud- 
ied and  described  by  Mr.  and  Mrs.  Peckham  (7). 
Ammophila  makes  a  small  hole  in  the  ground  and 
then  goes  out  to  hunt  for  a  caterpillar,  which,  when 
found,  it  paralyses  by  one  or  several  stings.  The 
wasp  carries  the  caterpillar  back  to  the  nest,  puts 
it  into  the  hole,  and  covers  it  with  sand.  Before  this 
is  done.  It  deposits  its  ^g<g  and  the  caterpillar  serves 
the  young  larva  as  food. 

I  will  describe  one  observation  on  the  means  these 


DISTRIBUTION  OF  MEMORY  225 

wasps  employ  of  finding  their  way  to  the  nest,  which 
absolutely  excludes  the  assumption  that  they  are 
guided  refiexly  by  known  or  unknown  stimuli,  and 
which  indicates  that  they  find  their  way  through 
memory.  An  Ammophila  had  a  hole  in  a  flower-bed 
in  my  front  yard.  The  wasp,  of  course,  left  the  yard 
flying.  Towards  noon  I  saw  an  Ammophila  running 
on  the  sidewalk  of  the  street  in  front  of  the  yard 
carrying  a  caterpillar  in  its  mouth.  The  weight  of 
the  caterpillar  prevented  it  from  flying.  The  yard 
is  separated  from  the  street  by  a  cemented  stone 
wall.  I  noticed  that  the  wasp  repeatedly  made  an 
attempt  to  climb  upon  the  wall,  but  kept  falling 
down.  Suspecting  that  it  might  have  its  nest  in 
the  yard  I  was  curious  to  see  whether  and  how  it 
would  find  the  nest. 

It  followed  the  wall  until  it  reached  the  neighbour- 
ing yard,  which  had  no  wall.  It  now  left  the  street 
and  crept  into  this  yard.  Then  crawling  through 
the  fence  which  separated  the  two  yards,  it  dropped 
the  caterpillar  near  the  foot  of  a  tree,  and  flew 
away.  After  a  short  zigzag  flight  it  alighted  on 
a  flower-bed  in  which  I  noticed  two  holes.  It  soon 
left  the  bed  and  flew  back  to  the  tree,  not  in  a 
straight  line  but  in  three  stages,  stopping  twice  on  its 
way.  At  the  third  stop  it  landed  at  the  place  where 
the  caterpillar  lay.  The  caterpillar  was  then  dragged 
to  the  hole,  pulled  into  it,  and  covered  with  sand. 

As  the  wasp  only  walks  to  the  hole  when  carrying 
a  caterpillar,  it  is  impossible  to  say  that  it  followed  a 


226  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

trace  and  was  guided  reflexly  when  It  carried  the  cat- 
erpillar to  the  nest.  The  repeated  attempts  to  climb 
the  wall  of  the  yard  which  first  attracted  my  atten- 
tion indicate  that  the  wasp  remembered  the  location 
of  the  nest.  The  fact  that  it  returned  to  fetch  the 
caterpillar  indicates  that  it  remembered  having 
dropped  it,  and  also  where  it  had  been  dropped.  The 
zigzag  character  of  its  flight  shows  that  it  was  not 
guided  reflexly. 

While  these  animals  without  doubt  possess  asso- 
ciative memory  they  possess  little  '*  intelligence." 

I  mentioned  that  the  Ammophila  covered  the  hole 
in  which  it  had  buried  the  caterpillar.  In  order  to 
cover  it,  the  wasp  had  to  pick  up  little  grains  of 
sand  in  the  neighbourhood  of  the  hole  and  carry  them 
in  its  mandibles  to  the  hole.  Once,  while  it  had  its 
back  turned  to  the  nest  and  was  picking  up  a  grain  of 
sand,  I  covered  the  hole  with  a  clover  blossom.  The 
wasp  was  no  longer  able  to  find  the  hole.  It  ran  and 
flew  about  in  the  most  excited  manner,  returning  each 
time  to  the  place  where  the  hole  had  been,  without 
being  able  to  discover  it.  I  finally  removed  the 
flower,  and  the  wasp  immediately  found  the  hole  and 
continued  covering  it  with  sand.  The  blossom  with 
which  I  covered  the  hole  weighed  considerably  less 
than  the  caterpillar  which  the  wasp  carried  with  such 
ease  between  its  mandibles.  The  fact  that  the  wasp 
kept  returning  to  the  spot  where  the  hole  was,  indi- 
cates again  the  existence  of  memory  in  these  animals. 

Bethe's  conclusions  have  been  criticised  by  Was- 


DISTRIBUTION  OF  MEMORY  227 

mann  (8)  as  far  as  ants,  and  by  von  Buttel-Reepen 
(9)  as  far  as  bees,  are  concerned.  I  think  that  bees 
and  ants  possess  associative  memory.  In  their  re- 
actions, however,  reflex  or  instinctive  elements  and 
memory  elements  are  mixed  together.  The  task  re- 
mains to  discover  how  much  of  a  r6le  associative 
memory  plays  in  the  various  habits  of  bees,  ants,  and 
wasps. 

6.  The  possibility  of  associative  memory  must  be 
conceded  in  the  case  of  spiders,  certain  Crustacea,  and 
Cephalopods,  but  it  is  in  all  probability  wanting  in 
!oelenterates  and  in  worms.  We  saw  that  Act- 
inians  refuse  water-soaked  paper  wads  and  take 
meat,  though  our  organs  of  taste  cannot  distinguish 
between  the  two.  Some  authors  would  have  called 
this  an  expression  of  intelligence  because  the  Actinian 
can  "discriminate"  and  **make  a  selection."  Accord- 
ing to  this,  consciousness  and  intelligence  should  be 
attributed  to  the  chemical  elements,  for  they  unite 
only  with  certain  other  elements.  The  term  "  power 
of  discrimination "  is  often  merely  an  ill-chosen  ex- 
pression for  the  fact  that  different  causes  have  differ- 
ent effects.  This  difference  of  the  effects  may  in  some 
cases  depend  on  associative  memory,  but  in  order  to 
find  out  these  cases  we  must  first  prove  that  the 
forms  under  consideration  have  associative  memory. 
In  Actinians,  however,  all  attempts  to  prove  the  exist- 
ence of  associative  memory  have  been  fruitless.  This 
is  shown  in  the  experiments  on  Cerianthus  mentioned 
above,  in  which  I  succeeded  in  producing,  below  the 


228  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

normal  head,  a  second  head,  which  had  an  oral  disc 
and  tentacles  but  no  mouth  (Fig.  12,  p.  52).  The  ten- 
tacles never  learned  that  no  mouth  was  present,  but 
continued  when  meat  was  offered  to  make  the  attempt 
to  force  it  into  an  opening  that  did  not  exist. 

Some  reactions  of  lower  animals  cannot  be  repeated 
indefinitely.  We  must  not  conclude,  however,  that 
this  is  due  to  processes  of  association  and  that  the 
animal  has  learned  certain  effects.  It  is  a  well-known 
fact  that  many  worms  that  live  in  cases  suddenly 
withdraw  into  their  cases  when  a  shadow  is  cast  on 
them.  I  analysed  this  process  and  showed  that  the 
shadow  has  nothing  to  do  with  the  phenomenon.  It 
is  due  to  a  reaction  against  negative  variations  in  the 
intensity  of  the  light,  comparable  to  the  ''  break-con- 
traction "  of  a  muscle.  The  experiment  does  not  suc- 
ceed if  repeated  an  indefinite  number  of  times  in 
succession.  Nagel  concludes  from  this  that  these 
worms  possess  "  the  ability  to  judge."  "  The  animal 
recognises  that  the  shadow  cast  so  frequently  does 
not  signify  the  approach  of  an  enemy  or  of  any  other 
danger"  (Nagel).  In  reality  these  reactions  are  in- 
herited forms  of  irritability  that  have  nothing  to  do 
with  experience.  The  reason  that  the  reaction  ceases 
if  repeated  frequently  is  due  to  a  simple  after-effect 
of  the  stimulus,  a  case  that  we  often  meet  in  the  physi- 
ology of  both  animals  and  plants.  The  assumption 
that  such  low  animals  as  eyeless  worms  and  snails 
possess  ideas  or  even  the  one  idea  of  *'  an  approach- 
ing enemy  or  other  impending  danger"  is  entirely 


i 


DISTRIBUTION  OF  MEMORY  229 

arbitrary.  Graber  also  maintained  that  animals  that 
go  to  the  light  do  so  because  they  love  it,  and  another 
author  thought  that  animals  fly  into  the  flame  out  of 
curiosity.  It  is  not  worth  while  to  follow  up  such  an- 
thropomorphisms in  the  biological  literature.  Biol- 
ogy is  as  much  justified  in  ignoring  them  as  modern 
physics  is  in  ignoring  the  fact  that  savages  explain 
the  locomotive  by  supposing  a  horse  to  be  concealed 
within  it.  On  the  contrary,  biology  should  concern 
itself  with  a  systematic  investigation  of  the  differ- 
ent animals  in  regard  to  the  existence  of  associative 
memory.  The  total  results  of  such  an  investigation 
will  furnish  the  material  for  a  future  comparative 
psychology. 

7.  Our  conception  meets  with  an  apparent  difficulty 
in  the  fact  that  stimuli  which  call  forth  sensations  of 
pain  in  us  produce  also  reactions  in  lower  animals 
which  have  no  memory.  These  reactions  are  natur- 
ally regarded  as  the  expression  of  sensations  of  pain. 
The  injured  worm  writhes  and  wriggles,  and  it  is  diffi- 
cult to  rid  ourselves  of  the  impression  that  these 
movements  are  the  expression  of  severe  pain.  Yet 
W.  W.  Norman  proved  that  this  conclusion  is  by  no 
means  justified  (5,  10).  He  found  that  if  an  earth- 
worm is  divided  transversely,  only  the  posterior  piece 
makes  these  writhing  movements,  while  the  anterior 
piece  crawls  off  as  if  nothing  had  happened.  It 
would,  of  course,  be  absurd  to  assume  that  the  pos- 
terior piece  alone  is  capable  of  a  sensation  of  pain, 
while   the    anterior  piece,  which  contains  the  brain, 


22,0  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

experiences  no  such  sensation.  If  we  continue  the  ex- 
periment and  divide  the  posterior  piece  in  the  middle, 
the  anterior  part  crawls  off  calmly  while  the  posterior 
part  again  makes  writhing  movements.  We  obtain 
the  same  results  if  we  divide  the  anterior  piece.  No 
matter  how  the  worm  is  divided,  the  piece  in  front 
of  the  place  of  division  shows  coordinated  crawling 
movements,  while  the  piece  behind  the  place  of  divis- 
ion makes  writhing  movements.  It  is  not  even  neces- 
sary to  cut  the  worm.  If  we  only  touch  it  with  the 
point  of  a  pencil  the  posterior  part  wriggles,  the  ante- 
rior part  elongates.  The  only  conclusion  that  can  be 
drawn  is  that  the  stimulus  of  cutting  produces  a  dif- 
ferent effect  when  it  extends  forward  through  the 
worm,  from  the  effect  which  it  produces  when  it  ex- 
tends backward.  The  movements  do  not  indicate 
that  the  animal  possesses  sensations  of  pain. 

Similar  observations  can  be  made  in  other  Annelids. 
In  Planarians  I  had  already  observed  that  they  give 
no  evidence  of  pain  when  they  are  divided  trans- 
versely. The  forward  piece  crawls  or  swims  as  if 
nothing  had  happened,  occasionally  merely  hasten- 
ing its  movements. 

But  even  in  insects  and  Crustaceans  pieces  can  be 
cut  off  without  any  reaction  from  the  animal  which 
might  be  interpreted  as  the  expression  of  a  pain- 
sensation. 

Janet  has  observed  that  the  abdomen  of  a  bee  can  be 
cut  off  while  the  bee  is  sucking  honey  without  causing 
any  interruption  in  its  occupation.     In  1888  I  noticed 


DISTRIBUTION  OF  MEMORY  231 

something  similar  in  a  small  Crustacean,  Gammarus, 
during  copulation.  The  abdomen  of  the  male  can  be 
cut  off  while  it  is  seated  on  the  female  without  caus- 
ing it  to  release  the  female.  In  fact,  unless  my  mem- 
ory deceives  me,  these  males  without  abdomen,  when 
torn  away  from  the  female,  were  ready  to  hold  another 
as  soon  as  they  could  find  one.  Norman  has  added 
a  great  many  similar  observations  on  insects  and 
Crustaceans  (10).  The  result  of  all  these  observa- 
tions is  that  either  these  Invertebrates  do  not  react 
to  injury  in  a  way  which  indicates  the  existence  of 
pain-sensation,  or  that,  if  there  seem  to  be  such  re- 
actions, they  do  not  justify  the  assumption  of  the 
existence  of  pain-sensations. 

We  cannot  be  surprised  that  among  those  repre- 
sentatives of  the  lower  Vertebrates  which  have  no 
associative  memory,  or  only  traces  of  it,  similar  con- 
ditions exist. 

Hermann  and  other  physiologists  maintain  that 
the  reactions  of  lower  Vertebrates  under  the  influence 
of  an  ascending  current  are  due  to  pain-sensations, 
while  the  descending  current  is  said  to  have  a  sooth- 
ing effect.  Garrey  and  I  came  to  the  conclusion  that, 
in  both  cases,  different  sets  of  muscles  were  thrown 
into  activity  (see  Chapter  XL).  In  order  to  test 
Hermann's  view,  we  experimented  on  larvae  of  Am- 
blystoma  whose  spinal  cord  had  been  cut  between  the 
head  and  the  tail-end  of  the  body.  We  found  that 
in  the  ascending  current  only  the  tail-end  of  the  ani- 
mal showed  those  reactions  which  Hermann  and  the 


232  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

Other  physiologists  had  considered  as  the  expression 
of  pain-sensations.  I  may  mention  further  that  when 
the  motions  following  the  stimulation  of  the  semicir- 
cular canals  were  first  observed  they  were  considered 
by  some  authors  as  the  expression  of  pain-sensations. 

Norman  observed  that  sharks  and  flounders  react 
in  no  way  against  very  severe  operations,  e.  g.,  the 
laying  bare  of  the  semicircular  canals,  provided  that 
respiration  was  not  interfered  with  (lo).  As  soon 
as  the  water-supply  to  the  mouth  was  cut  off,  they 
made  violent  motions,  which  are  characteristic  for  the 
condition  of  beginning  asphyxiation  and  which  have 
nothing  in  common  with  conscious  acts.  Sharks  and 
flounders  belong  to  that  class  of  Vertebrates  which 
have  practically  no  associative  memory. 

It  therefore  seems  to  me  that  our  experience  con- 
cerning the  pain-sensations  of  animals  does  not  con- 
tradict our  view  regarding  the  limits  of  associative 
memory  or  the  consciousness  of  the  metaphysicians. 

Of  course  I  do  not  expect  to  convince  the  senti- 
mentalists and  Darwinians.  The  former  will  say  that 
their  "  feeling "  tells  them  that  an  earthworm  is 
capable  of  pain-sensations.  My  reply  to  these  is 
that  the  burden  of  proof  rests  upon  them.  If  a  per- 
son maintains  that  there  is  a  gaseous  Vertebrate  in 
the  air  it  is  plainly  his  duty  to  prove  its  existence,  and 
not  the  duty  of  all  the  other  scientists  to  disprove  it. 
Otherwise  we  might  be  called  upon  to  waste  our  lives 
in  disproving  the  statements  of  any  insane  person  or 
impostor.     The  Darwinians  will  doubt  the  possibility 


DISTRIBUTION  OF  MEMORY  233 

that  pain-sensations  or  any  definite  characters  should 
appear  in  certain  forms  without  existing  (although  in 
a  rudimentary  form)  in  the  whole  animal  kingdom. 
To  these  we  shall  reply  in  the  next  chapter  (p.  251). 
8.  At  the  end  of  the  chapter  on  instincts  we 
mentioned  that  in  those  animals  which  possess  asso- 
ciative memory  the  instinctive  reactions  may  be 
modified  or  complicated  by  the  influence  of  the 
associations.  This  influence  can  be  so  powerful  that 
the  instincts  are  warped  or  suppressed  altogether. 
By  education  and  experience  the  memory  of  man  is 
filled  with  a  number  of  associations  which  can  inhibit 
any  reflex  or  instinctive  motor  process.  To  a  certain 
extent  these  inhibitory  associations  are  necessary  for 
the  preservation  of  the  life  of  the  individual.  More- 
over, it  is  necessary  to  provide  the  child  with  associa- 
tions which  prevent  ''dissipation,"  e.g.,  the  cultivation 
of  one  or  a  few  instincts  at  the  expense  of  others. 
The  greatest  happiness  in  life  can  be  obtained  only 
if  all  the  instincts — that  of  workmanship  included — 
can  be  maintained  at  a  certain  optimal  intensity.  But 
while  it  is  certain  that  the  individual  can  ruin  or  di- 
minish the  value  of  its  life  by  a  one-sided  develop- 
ment of  its  instincts — e.  g.,  dissipation, — it  is  at  the 
same  time  true  that  the  economic  and  social  condi- 
tions can  ruin  or  diminish  the  value  of  life  for  a  great 
number  of  individuals.^ 

*  It  is  no  doubt  true  that  in  our  present  social  and  economic  condition  more 
than  ninety  per  cent,  of  human  beings  lead  an  existence  whose  value  is  far  be- 
low what  it  should  be.  They  are  compelled  by  want  ta  sacrifice  a  number  of 
instincts,  especially  the  most  valuable  among  them,  that  of  workmanship,  in 


234  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

Although  we  recognise  no  metaphysical  free-will, 
we  do  not  deny  personal  responsibility.  We  can  fill 
the  memory  of  the  young  generation  with  such  asso- 
ciations as  will  prevent  wrongdoing  or  dissipation. 
If  in  a  human  being  such  associations  are  lacking,  it 
points  to  an  organic  deficiency  or  to  an  insui^cient 
education,  for  which  in  some  cases  the  parents,  in  the 
majority  of  cases,  our  present  social  conditions,  are 
responsible. 

Punishment  is,  perhaps,  justifiable  in  so  far  as  it 
may  bring  about  inhibitory  associations  or  may  be 
able  to  strengthen  the  inhibitory  associations  of 
weaker  members  of  society.  Inhibitions  to  be  effect- 
ive, however,  must  be  cultivated  in  youth,  as  the  time 
at  which  the  penal  code  is  enforced  is  usually  too  late 
for  any  lasting  benefit.  Cruelty  in  the  penal  code 
and  the  tendency  to  exaggerate  punishments  are  sure 
signs  of  a  low  civilisation  and  of  an  imperfect 
educational  system. 

order  to  save  the  lowest  and  most  imperative,  that  of  eating.  If  those  who 
amass  immense  fortunes  could  possibly  intensify  their  own  lives  with  their  abun- 
dance, it  might  perhaps  be  rational  to  let  many  suffer  in  order  to  have  a  few 
cases  of  true  happiness.  But  for  an  increase  of  happiness  only  that  amount  of 
money  is  of  service  which  can  be  used  for  the  harmonious  development  and 
satisfaction  of  inherited  instincts.  For  this  comparatively  little  is  necessary. 
The  rest  is  of  no  more  use  to  a  man  than  the  surplus  of  oxygen  in  the  atmos- 
phere. As  a  matter  of  fact,  the  only  true  satisfaction  a  multi-millionaire  can 
possibly  get  from  increasing  his  fortune,  is  the  satisfaction  of  the  instinct  of 
workmanship,  or  the  pleasure  that  is  connected  with  a  successful  display 
of  energy.  The  scientist  gets  this  satisfaction  without  diminishing  the  value 
of  life  of  his  fellow-beings,  and  the  same  should  be  true  for  the  business  man. 


DISTRIBUTION  OF  MEMORY  235 

Bibliography. 

1.  Mach,  E.  Contributions  to  the  Analysis  of  the  Sensations. 
The  Open  Court  Publishing  Co.,  Chicago,  1897, 

2.  LoEB,  J,  Beitrdge  zur  Gehirnphysiologie  der  Wiirmer. 
Fflugers  Archiv^  Bd.  Ivi.,  1894.  Zur  Psychologie  und  Physiologic 
der  Aktinien.  PJluger's  Archiv^  Bd.  lix.,  1896.  Zur  Theorie  der 
physiologischen  Licht-  und  Schwerkraftwirkungen.  Pfluger's 
Archiv,  Bd.  Ixvi.,  1897. 

3.  LoEB,  J.  Weitere  Bemerkungen  ilber  den  Heliotropismus  der 
Thiere  und  seine  Uebereinstitnmung  mit  dent  Heliotropismus  der 
Pflanzen.     PlUger  s  Archiv,  Bd.  xlvii. 

4.  Bethe,  a.  Diirfen  wir  den  Ameisen  und  den  Bienen psychische 
Qualitdten  zuschreiben?     Pfliiger's  Archiv^  Bd.  Ixx.,  1898. 

5.  Norman,  W.  W.  Diirfen  wir  aus  den  Reactionen  niederer 
Thiere  auf  Schmerzempfindungen  derselben  schliessen?  Pfiilger's 
Archil^  Bd.  Ixvii.,  1897. 

6.  MuNSTERBERG,  H.     Die  Willenshandlung.     Freiburg,  1888. 

7.  Peckham,  G.  W.  and  E.  G.  On  the  Instincts  and  Habits  of 
the  Solitary  Wasps.  Wisconsin  Geological  and  Natural  History 
Survey^  1898. 

8.  Wasmann,  E.  Die  psychischen  Fdhigkeiten  der  Ameisen. 
Zoologica^  vol.  xi.,  1899. 

9.  V.  Buttel-Reepen.  Sind  die  Bienen  Reflexmaschinen? 
Biologisches  Centralblatt^  vol.  xx.,  1900. 

10.  Norman,  W.  W.  Do  the  Reactions  of  the  Lower  Animals 
against  Injury  Indicate  Pain- Sensations  ?  The  American  J^ourn.  of 
Physiology^  vol.  iii.,  1900. 

1 1.  Mach,  E.  Die  Analyse  der  Empfindungen  und  das  Verhdlt- 
niss  des  Physischen  zum  Psychischen.     Jena,  1900. 

12.  James,  W.     The  Principles  of  Psychology.   New  York,  1890. 


CHAPTER  XVI 

CEREBRAL    HEMISPHERES     AND     ASSOCIATIVE 

MEMORY 

I.  The  view  that  consciousness  is  only  a  meta- 
physical term  for  the  phenomena  determined  by  the 
mechanisms  of  associative  memory  finds  support  in 
the  results  of  experiments  on  higher  animals.  Extir- 
pation of  the  cerebral  hemispheres  causes  complete 
loss  of  associative  memory.  After  this  operation,  no- 
thing remains  that  could  possibly  be  interpreted  by 
the  metaphysicians  as  a  phenomenon  of  consciousness. 

If  the  cerebral  hemispheres  of  a  Rana  esculenta  or 
temporaria  be  extirpated,  the  frog  seems  on  the  whole 
to  be  unchanged.  This  has  been  proved  beyond 
question  by  Schrader  (i).  Such  a  frog  catches  flies, 
buries  itself  in  the  mud  when  the  cold  season  comes, 
and  changes  its  habitation  from  the  land  to  the  water, 
like  a  normal  frog.  None  of  these  processes,  how- 
ever, are  functions  of  associative  memory  ;  they  de- 
pend upon  inherited  structures.  The  frog  either  has 
no  associative  memory  or  it  is  so  insignificant  that  it 
does  not  in  any  way  affect  the  behaviour  of  the  frog. 
This  explains  the  fact  that  the  loss  of  the  cerebral 

236 


CEREBRAL  HEMISPHERES  AND  MEMORY  237 

hemispheres,  which  produces  so  great  a  change  in  the 
personality  of  a  higher  animal,  has  much  less  effect  on 
a  frog.  In  the  shark,  nothing  in  the  habits  or  reac- 
tions of  the  normal  animal  shows  the  existence  of 
associative  memory.  Most  of  its  reactions  are  inher- 
ited and  composed  of  segmental  reflexes.  We  find, 
correspondingly,  that  it  shows  very  little  change  after 
the  extirpation  of  the  cerebral  hemispheres,  for  in 
spite  of  their  loss  the  segmental  reflexes  are  pre- 
served. 

It  would  be  a  mistake  to  assume  that  the  loss  of  the 
cerebral  hemispheres  in  no  way  affects  the  animal. 
Its  loss  has  a  certain  effect  upon  the  segmental  re- 
flexes. Nereis  has  no  associative  memory,  yet  it  shows 
a  certain  lack  of  inhibition  after  the  loss  of  the  supra- 
cesophageal  ganglion  (see  Chapter  VI.).  Something 
similar  is  noticeable  in  lower  Vertebrates  whose  cere- 
bral hemispheres  are  removed.  For  instance,  in  ad- 
ders all  segmental  reflexes  are  preserved  after  loss  of 
the  cerebral  hemispheres.  Schrader  found,  however, 
that  such  animals  no  longer  show  any  "  fear  " — it  was 
not  possible  to  frighten  them  although  all  the  opticus- 
reflexes  still  functioned  (2).  From  this  we  must  con- 
clude that  the  effects  of  those  stimuli  which  extend 
from  the  opticus-segment  into  the  central  nervous 
system  are  different,  so  long  as  the  cerebral  hemi- 
spheres exist,  from  what  they  are  when  the  hemi- 
spheres have  been  extirpated.  Something  of  this 
kind  also  shows  itself  in  the  frog.  Goltz  has  found 
that  the  frog  without  cerebral  hemispheres  is  better 


238  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

suited  for  demonstrating  reflexes  than  the  frog  with 
cerebral  hemispheres.  If  the  skin  on  the  back  of 
a  normal  frog  is  touched,  it  may  or  may  not  croak. 
Goltz  showed  that  this  croaking  reflex  never  fails  in  a 
frog  whose  cerebral  hemispheres  have  been  excised 
(3).  In  the  normal  frog,  however,  touching  the  skin 
of  the  back  produces,  in  addition,  another  reflex  :  it 
shows  a  tendency  to  leap  away.  The  normal  frog  as 
well  as  the  frog  without  cerebral  hemispheres  is  a  re- 
flex animal — that  is,  its  reactions  are  chiefly  segmen- 
tal reflexes.  But  there  is  this  difference  between  the 
two  :  In  the  animal  with  cerebral  hemispheres  the 
same  stimulus  can  produce  more  than  a  single  reflex, 
and  this  fact  adds  to  the  greater  complication  and 
capriciousness  of  the  reactions  of  the  animal.  On  the 
other  hand,  the  cerebral  hemispheres  can  also  restrict 
the  play  of  the  segmental  reflexes.  The  clasping  re- 
flex of  the  male  frog  in  the  act  of  copulation  is  a 
segmental  reflex  of  the  arm-segments  during  the 
period  of  heat.  It  seems  that  sexual  substances  de- 
termine this  reflex,  since  it  cannot  be  shown  to  exist 
in  animals  that  are  castrated  before  the  period  of 
heat.  Now  male  frogs  that  have  lost  the  cerebral 
hemispheres  are  much  more  indifferent  in  the  choice 
of  the  object  they  clasp  during  the  period  of  heat 
than  animals  with  cerebral  hemispheres. 

2.  In  birds  the  conditions  are  different  from  those 
which  exist  in  frogs  and  sharks.  We  are  indebted  to 
Schrader  for  an  exact  and,  in  many  respects,  classic 
investigation  of  the  effect  of  the  extirpation  of  the 


CEREBRAL  HEMISPHERES  AND  MEMORY    239 

cerebral  hemispheres  on  birds  (4).  The  work  of  this 
investigator,  Goltz's  article  on  the  dog  without  cere- 
bral hemispheres,  and  Goltz's  and  Ewald's  article  on 
the  dog  with  shortened  spinal  cord  are  among  the 
best  on  the  physiology  of  the  central  nervous  system. 
Until  their  work  appeared,  it  was  a  dogma  (and  is 
still  in  many  text-books)  that  animals  which  have  lost 
the  cerebral  hemispheres  can  no  longer  move  spon- 
taneously. Flourens  is  responsible  for  the  statement. 
Schrader  first  disproved  it  in  regard  to  the  frog  and 
then  succeeded  in  disproving  it  in  the  case  of  birds. 
**  None  of  the  animals  under  observation  [pigeons] 
showed  a  sleep-like  condition  longer  than  three  to 
four  days  [after  excision  of  the  cerebral  hemispheres]. 
According  to  Rolando  and  Flourens,  animals  which 
have  undergone  this  operation,  except  when  certain 
stimuli  are  applied  to  the  skin,  remain  absolutely 
quiet.  At  first,  this  is  true.  The  pigeons  remain 
standing,  where  they  are  placed,  with  ruffled  feathers, 
the  head  drawn  in,  the  eyes  closed,  and  often  on  one 
leg.  Occasionally  they  shake  themselves,  clean  their 
feathers  with  their  beak,  stretch  sleepily,  and  in  the 
act  of  defsecation  take  a  few  steps.  If  left  undis- 
turbed, nothing  else  is  to  be  observed.  When  thrown 
up  into  the  air,  they  fly  down  diagonally,  strike  ob- 
stacles, and  fall  rather  than  alight  on  the  floor,  where 
they  at  once  sink  back  into  their  stupor  again.  If 
the  skin  is  stimulated,  they  take  a  few  steps,  but  in  so 
doing  are  liable  to  run  into  obstacles"  (Schrader, 
loc,  cit.). 


240  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

The  difference  between  Flourens's  and  Schrader's 
observations  lies  in  the  fact  that  Flourens  considered 
this  condition  permanent,  while  Schrader  showed  that 
it  lasts  only  a  few  days  or  until  the  ''  shock-effect  "  of 
the  operation  has  passed  off.  The  objection  might 
be  raised  that  Schrader  did  not  entirely  remove  the 
hemispheres,  but  this  was  not  the  case.  Schrader's 
experiments  are  masterpieces  in  regard  to  the  perfec- 
tion of  the  mode  of  operation.  The  contradiction  in 
the  statements  of  the  two  authors  is  due  to  the  fact, 
as  it  so  often  is  in  brain-physiology,  that  the  minor 
effects  of  the  operation  in  one  case  were  strong,  in 
the  other  slight,  or  that  one  author  based  his  opinion 
upon  the  most  severe  disturbances,  the  other  upon 
the  slightest  disturbances.  The  latter  is  the  only  re- 
liable method  in  physiology  of  the  brain,  because  in 
addition  to  the  disturbances  caused  by  the  loss  of 
part  of  the  brain,  the  shock-effects  on  the  rest  of  the 
central  nervous  system  also  appear  in  the  mosaic  of 
symptoms.  Schrader's  experiments  are  models  in 
regard  to  technique,  but  this  cannot  be  said  of 
Flourens's  experiment,  to  which  fact  the  excellent 
investigator  Magendie  vainly  called  attention. 

In  Schrader's  experiments,  a  few  days  after  the 
operation,  spontaneity  not  only  returns^  but  is  even  in- 
creased. The  animal  wanders  about  in  the  room  un- 
tiringly the  greater  part  of  the  day.  It  is  not  blind, 
for  its  movements  are  determined  by  visual  impres- 
sions. Like  the  frog  without  cerebral  hemispheres,  it 
turns  out  to  avoid  obstacles.     ''  Dusty  window-glass, 


CEREBRAL  HEMISPHERES  AND  MEMORY   241 

transparent  bell-jars  placed  in  their  way  were  avoided 
just  as  much  as  chairs  and  table  legs,  or  boards  of 
different  colours."  It  is  evident  that  optic  space-per- 
ception still  continues,  even  when  the  cerebral  hemi- 
spheres (and  with  them  the  associative  memory)  have 
disappeared  entirely.  If  such  a  pigeon  is  placed  in 
an  uncomfortable  position,  it  flies  to  another  place 
with  perfectly  coordinated  movements.  Schrader 
gives  the  following  description  :  **  We  place  our 
pigeon  on  the  cloth-covered  stopper  of  a  large  bottle. 
The  stopper  is  large  enough  to  support  the  animal  on 
both  feet,  and  Is  placed  in  the  middle  of  a  large,  empty 
room,  so  that  the  pigeon  is  one  to  two  metres  above 
the  floor.  For  some  minutes  the  pigeon  sits  with  its 
head  drawn  in,  its  feathers  ruffled,  in  a  condition  of 
sleep  or  inhibition  ;  then  it  shakes  itself  and  begins  to 
turn  around  and  look  about ;  finally  it  stoops  and  with 
an  exertion  looks  down  on  the  floor  as  if  it  wished  to 
measure  the  height.  It  makes  preparations  to  fly 
down,  stops  again,  however,  turns  about  once  more, 
and  again  directs  its  attention  to  the  floor.  The  dura- 
tion of  this  play  varies,  but  at  last  it  flies  down  in  a 
slight  curve  and  alights  easily  on  the  floor.  If  a 
cross-bar  is  placed  at  the  same  height,  one  or  two 
metres  from  the  bottle,  the  pigeon  flies  determinedly 
to  the  bar  and  seats  itself  there.  If  a  chair  be  used 
instead  of  a  bar,  the  pigeon  is  seated  on  the  arm  "  (4). 
These  experiments  show  that  these  pigeons  are  able 
to  measure  distance  by  visual  impressions  also. 

Schrader  s  observation  is  also  of  importance  for  the 


242  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

solving  of  the  problem  as  to  whether  sensations  of 
space  are  purely  a  matter  of  memory,  as  Helmholtz, 
among  others,  assumes,  or  whether  they  are  deter- 
mined by  inherited  structural  conditions,  as  Hering, 
for  instance,  maintains.  The  question  is  of  great  im- 
portance for  the  further  investigation  of  the  mechanics 
of  the  brain,  and  for  this  reason  we  mention  it  in 
passing.  It  has  been  assumed  that  space-sensations 
are  acquired  because  the  new-born  infant  does  not 
immediately  show  signs  of  orientation  in  space.  The 
fact  is  overlooked  that  the  new-born  infant  comes  into 
the  world  incomplete — that  is  to  say,  certain  structures 
become  complete  during  the  first  year  or  even  later. 
The  same  erroneous  conclusion  was  drawn  in  regard 
to  walking.  The  child  was  supposed  to  *'  learn  "  to 
walk.  The  fact  that  the  chick  can  walk  when  it 
comes  out  of  the  ^'g^  would  have  sufficed  to  prevent 
this  error  on  the  part  of  the  empiricists,  if  physiolo- 
gists had  earlier  appreciated  the  importance  of  com- 
parative physiology.  The  difference  between  the 
chick  and  the  human  suckling  consists  in  the  fact  that 
the  structural  development  of  the  former  is  more 
complete  at  the  moment  of  hatching  than  the  struct- 
ural development  of  the  latter  at  the  time  of  its 
birth.  The  child  can  begin  to  walk  only  when  the 
nerves,  muscles,  etc.,  have  reached  the  required  de- 
gree of  development.  The  same  is  true  of  visual 
space-perception.  The  newly  hatched  chick  has  vis- 
ual perception  ;  that  is,  it  picks  at  points  that  differ 
from  their  environment  in  colour  and  intensity  of  light. 


CEREBRAL  HEMISPHERES  AND  MEMORY   243 

It  does  not  learn  this  reaction  any  more  than  a  plant 
learns  its  heliotropic  reactions,  and  it  is  no  more 
necessary  for  the  suckling  than  for  the  chick  to  learn 
space-reactions.  They  come  *'  of  themselves  "  as  soon 
as  the  embryonic  development  of  the  suckling  has  ad- 
vanced far  enough.  This  conception,  to  which  com- 
parative physiology  forces  us,  is  further  supported 
most  effectually  by  Schrader's  observation  (and  by 
those  of  earlier  authors,  for  instance,  Longet)  that 
visual  space-perception  in  birds  continues  after  the 
cerebral  hemispheres  have  been  removed.  The  pos- 
sibility that  this  holds  good  for  birds  and  not  for 
mammals  is  refuted  by  a  statement  of  Christiani  in 
regard  to  rabbits.  The  fact,  however,  that  space- 
reactions  can  be  modified  by  the  memory,  that  we 
can  **  learn  "  to  shave  before  a  mirror,  for  instance, 
or  can  *'  learn  "  to  grasp  things  in  spite  of  prismatic 
glasses,  does  not  contradict  this  conception  any  more 
than  the  acquired  accomplishments  of  the  dancer  con- 
tradict the  fact  that  normal  walking  is  not  a  matter 
of  memory.  The  fact  that  coordinated  progressive 
movements  on  the  turn-table  occur  in  the  direction  of 
the  plane  of  the  rotation,  and  those  produced  by  a  gal- 
vanic current  occur  in  the  direction  of  the  curves  of 
the  current,  also  speaks  for  this  nativistic  conception. 
From  this  digression  we  will  now  return  to  Schra- 
der's experiments.  The  pigeon  described  above  as 
wandering  about  the  room  all  day,  sleeps  at  night. 
Sleep  has  nothing  to  do  with  consciousness  and  mem- 
ory, for  it  occurs  in  plants.     It  is  not  surprising  then 


244  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

that  the  animal  without  cerebral  hemispheres  shows 
the  difference  between  sleeping  and  waking. 

The  g-reat  difference  between  the  normal  male 
pigeon  and  the  pigeon  that  has  lost  its  cerebral  hemi- 
spheres is  shown  forcibly  by  the  following  facts : 
During  the  period  of  heat  the  male  pigeon  courts  the 
female  with  cooing,  but  if  a  female  pigeon  is  placed 
before  the  cooing  male  whose  hemispheres  have  been 
removed,  it  remains  unheeded.  This  entire  lack  of 
memory  is  the  chief  point  in  which  the  animal  without 
cerebrum  differs  from  the  normal  animal.  *'  For  the 
former  everything  is  only  a  mass  in  space,  it  moves 
aside  for  every  pigeon  or  attempts  to  climb  over  it, 
just  as  it  would  in  the  case  of  a  stone.  All  authors 
agree  in  the  statement  that  to  these  animals  all  objects 
are  alike.  They  have  no  enemies  and  no  friends. 
They  live  like  hermits  no  matter  in  how  large  a  com- 
pany they  find  themselves.  The  languishing  coo  of 
the  male  makes  as  little  impression  upon  the  female 
deprived  of  its  cerebrum  as  the  rattling  of  peas  or  the 
whistle  which  formerly  made  it  hasten  to  its  feeding 
place.  Neither  does  the  female  show  interest  in  its 
young.  The  young  ones  that  have  just  learned  to  fly 
pursue  the  mother,  crying  unceasingly  for  food,  but 
they  might  as  well  beg  food  of  a  stone  "  (4). 

Taking  all  the  reactions  of  the  pigeon  without 
cerebral  hemispheres  together,  it  seems  to  me  that 
the  conclusion  may  be  drawn  that  loss  of  the  cerebral 
hemispheres  causes  the  loss  of  the  associative  mem- 
ory.    Inherited  reactions  remain  after  the  loss  of  the 


CEREBRAL  HEMISPHERES  AND  MEMORY   245 

cerebrum,  but  that  which  is  acquired  by  the  activity 
of  memory  during  the  Hfe  of  the  individual  is  lost 
forever. 

In  order  to  emphasise  this  loss  of  memory  after  ex- 
tirpation of  the  hemispheres,  we  will  quote  the  follow- 
ing observation  made  by  Schrader  on  a  falcon.  The 
falcon,  as  everyone  knows,  is  a  good  hunter.  Schrader 
placed  some  mice,  and  a  falcon  from  which  the  hemi- 
spheres had  been  removed  in  the  same  cage.  Every 
time  that  a  mouse  moved  the  falcon  jumped  on  it  and 
caught  it  in  its  claws,  if  the  movement  occurred  with- 
in its  field  of  vision.  The  normal  falcon  in  such  cases 
devours  the  mouse,  but  for  the  falcon  without  cerebral 
hemispheres  the  matter  was  at  an  end  when  the  mouse 
was  caught.  The  activity  of  the  associative  memory 
was  lacking  and  the  mouse  was  forgotten  as  soon  as  it 
ceased  to  move.  When  the  falcon  moved,  the  mouse 
escaped,  but  if  the  mouse  moved  again  the  process  was 
repeated.  Any  inanimate  object  that  moved  would,  of 
course,  be  caught  in  the  same  way.  The  falcon  and 
mice  remained  together  until  one  day  the  mouse  de- 
voured the  back  of  the  living  falcon.  Deprived  of  its 
memory  the  falcon  was  entirely  defenceless  (2). 

One  disturbance  takes  place  in  animals  that  have 
lost  the  cerebrum  which  does  not  belong  in  the  same 
class  with  disturbances  of  memory,  namely,  the  inabil- 
ity to  take  food  unassisted.  In  frogs  and,  according 
to  Steiner's  observations,  also  in  fishes  (5),  the  ability 
to  take  food  independently  continues  to  exist  after 
excision  of  the  cerebral  hemispheres.     Birds  without 


246  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

cerebral  hemispheres  starve  unless  they  are  fed. 
Schrader  came  to  the  conclusion  that  this  is  due  to  a 
disturbance  of  the  motor  innervation,  for  they  are  un- 
able to  swallow  a  pea  placed  in  the  front  part  of  the 
beak ;  to  be  swallowed  it  must  be  placed  well  back 
toward  the  throat  From  the  results  of  these  experi- 
ments on  frogs,  I  believe  that  we  might  go  one  step 
farther  than  Schrader  and  conclude  that,  in  this  case, 
the  tension  is  decreased  in  certain  groups  of  muscles 
which  are  necessary  for  taking  food  independently. 
We  shall  again  meet  with  such  a  decrease  in  the  ten- 
sion of  certain  muscles  after  lesion  of  the  cerebral 
hemispheres.  This  decrease  in  tension  is,  however,  a 
secondary  effect  of  the  operation  on  the  remaining 
segmental  tracts  of  the  central  nervous  system,  and  is 
not  determined  by  loss  of  the  cerebrum.  It  is  very 
probable  too  that  if  Schrader's  experiments  are  con- 
tinued birds  may  be  found  in  which  disturbances  in 
eating  will  not  occur. 

3.  The  bold  attempt  to  remove  both  hemispheres 
entirely  from  a  full-grown  dog  and  then  to  keep  it 
alive  not  only  for  months  but  for  years  has  been 
attempted  and  carried  on  successfully  by  Goltz  (6). 
The  results  of  his  experiments  in  a  few  words  are  as 
follows  :  In  such  a  dog  all  those  reactions  in  which  the 
associative  memory  plays  a  rdle  are  lacking  perma- 
nently, while  the  simple  reactions  that  only  depend  on 
inherited  conditions  remain  just  as  in  pigeons  and  in 
other  animals. 

The  dog  without  cerebral  hemispheres  sleeps  and 


CEREBRAL  HEMISPHERES  AND  MEMORY    247 

wakes.  It  moves  spontaneously — that  is,  without  visi- 
ble external  stimulus.  The  only  abnormal  feature  in 
the  progressive  movements  of  the  dog  without  cere- 
bral hemispheres  was  its  extreme  restlessness.  When 
not  asleep  it  moved  about  in  the  cage  unceasingly, 
and  this  perhaps  accounts  for  the  fact  that  such  ani- 
mals show  a  tendency  to  lose  flesh.  The  postures 
peculiar  to  dogs  in  urinating  and  defaecation  were  still 
assumed  by  these  dogs.  The  reactions  to  sensory 
stimuli  were  normal  in  so  far  as  no  associative  mem- 
ory was  necessary.  Meat  and  milk  were  devoured 
greedily,  but  if  made  bitter  with  quinine  they  were 
ejected.  The  dog  growled  and  snapped  if  its  paw  was 
pinched.  If  its  foot  was  placed  in  cold  water  it  was 
removed  at  once.  If  one  paw  was  injured  the  dog 
was  still  able  to  go  on  three  legs.  If  it  was  asleep  it 
could  be  waked  by  blowing  a  horn  in  the  next  room. 
If  in  a  dark  room  it  closed  its  eyes  when  a  strong 
light  was  suddenly  allowed  to  strike  it.  It  seemed 
more  wide-awake  and  restless  when  it  was  hungry  and 
more  quiet  after  it  had  been  fed.  In  regard  to  eating, 
the  dog  without  cerebral  hemispheres  was  more  nor- 
mal than  Schrader's  doves.  To  make  the  dog  eat,  it 
was  only  necessary  to  hold  the  plate  up  to  its  nose,  so 
that  the  nose  came  in  contact  with  the  meat.  The 
facts  that  motor  disturbances  exist  and  that  such 
dogs  do  not  turn  out  for  obstacles,  behaving  in  this 
regard  like  blind  dogs,  may  be  regarded  as  shock- 
effects  on  the  brachial  and  optic  segments,  produced  by 
the  operation.     The  dog  could  still  bark  and  howl. 


248  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

But  everything  requiring  associative  memory  was 
gone.  The  dog  was  not  able  to  seek  its  food.  It 
recognised  neither  its  master  nor  its  playmates.  It 
could  hear  but  could  not  discriminate  between  scold- 
ing and  petting.  It  was  impossible  for  it  to  get  itself 
out  of  any  uncomfortable  situation.  The  period  of 
heat  was  no  longer  noticeable.  The  effects  are  simi- 
lar to  those  upon  pigeons,  with  the  difference  that  the 
secondary  effects  of  the  operation  on  the  remaining 
parts  of  the  central  nervous  system  are  greater  in 
dogs.  The  reasons  for  this  may  be  purely  technical 
or  anatomical,  or  may  be  due  to  a  greater  sensitive- 
ness of  the  central  nervous  system  in  dogs.  We  may 
mention  in  this  connection  that  hemorrhages  in  the 
human  cerebral  hemispheres  are  often  accompanied 
by  a  complete  paralysis  of  the  extremities,  while  this 
is  never  the  case  in  dogs. 

The  fact  that  in  animals  which  normally  possess  no 
memory,  loss  of  the  hemispheres  occasions  little  dis- 
turbance, and  the  fact  that  in  animals  possessing 
memory,  the  latter  disappears  upon  destruction  of  the 
hemispheres,  prove  that  the  hemispheres  are  an  essen- 
tial organ  for  the  phenomena  of  associative  memory. 

4.  Pfluger  expressed  the  opinion  many  years  ago 
that  an  animal  that  has  lost  its  brain  still  possesses 
consciousness  (7).  He  drew  this  conclusion  from  the 
reactions  of  decapitated  animals.  If  the  tail  of  a  de- 
capitated eel  be  rubbed  gently  on  one  side  the  tail 
presses  itself  against  the  finger,  but  if  touched  with  a 
burning  match  it  is  turned  away.     From  these  and 


CEREBRAL  HEMISPHERES  AND  MEMORY   249 

similar  observations,  which  are  doubtless  correct, 
Pfluger  concluded  that  the  spinal  cord  possesses  con. 
sciousness.  Pfluger's  statements  gave  rise  to  a  lively- 
discussion.  His  opponents  could  not  refute  his  con- 
clusions entirely,  but  they  advanced  arguments  to  show 
that  the  spinal  cord  does  not  possess  consciousness. 
Goltz's  ingenious  experiments  deserve  special  mention 
in  this  connection  (3).  They  show  that  the  decapi- 
tated frog  is  not  able  to  rescue  itself  from  an  unpleas- 
ant situation.  A  blinded  but  otherwise  normal  frog 
and  a  frog  without  cerebral  hemispheres  were  placed 
together  in  a  trough  filled  with  water  and  the  water 
heated  gradually.  When  the  temperature  of  the  water 
rose,  the  blinded  frog  became  restless,  jumped  about, 
and  attempted  to  escape  from  the  trough.  The  frog 
without  cerebral  hemispheres,  on  the  other  hand,  re- 
mained quiet  and  the  heat  rigor  overcame  it  in  the 
attitude  it  assumed  when  put  into  the  trough.  This 
of  course  speaks  against  the  presence  of  consciousness 
in  the  spinal  cord.  But  since  this  did  not  directly 
prove  the  erroneousness  of  Pfluger's  conclusions,  opin- 
ions remained  divided.  I  believe  we  are  now  in  a 
position  to  prove  that  Pfluger's  observations  not  only 
allow  but  demand  an  entirely  different  explanation,  and 
that  it  is  wrong  to  make  them  a  criterion  for  the  exist- 
ence of  consciousness.  The  experiment  with  the  tail 
of  the  eel  is  a  case  of  tropism.  The  eel  is  positively 
stereotropic.  It  is  forced  to  bring  every  part  of  its 
body  as  far  as  possible  in  contact  with  solid  bodies, 
like  Nereis,  many  insects,  the   stolons   of  Hydroids, 


250  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

and  the  roots  of  many  plants.  It  lives  chiefly  in 
cracks.  This  is  no  more  a  process  of  consciousness 
than  the  boring  of  a  root  in  the  sand.  It  exists  in 
every  segment  of  the  eel,  and  if  touched  on  one  side 
with  the  finger  positively  stereotropic  curvations 
toward  the  finger  ensue.  The  stimulus  of  rubbing 
increases  the  tension  of  the  muscles  on  the  stimulated 
side.  But  while  it  is  positively  stereotropic  it  is  not 
positively  thermotropic.  If  a  burning  object  is  applied 
it  produces  a  relaxation  of  those  muscles  which  move 
the  body  toward  the  stimulated  side.^  The  body  is 
thus  moved  toward  the  opposite  side.  In  this  case 
too  consciousness  plays  no  more  part  than  it  does  in 
the  tropic  reactions  of  a  plant.  The  whole  discussion 
of  the  *'  spinal-cord-soul  "  was  needless,  and  might  have 
been  avoided  if  Pfliiger  had  realised  that  those  phe- 
nomena which  the  metaphysician  calls  consciousness 
are  a  function  of  the  mechanism  of  associative  mem- 
ory. In  that  case  the  question  would  have  been  : — 
Does  the  decapitated  animal  still  possess  associative 
memory,  or  are  its  reactions  all  due  to  inherited  struct- 
ures and  irritabilities  ?  With  the  aid  of  comparative 
physiology  it  would  have  been  found  that  all  the  reac- 
tions of  such  an  animal  may  occur  in  forms  which 
possess  no  associative  memory.  The  mechanisms 
which  allow  an  associative  memory  in  Vertebrates 
seem  to  be  located  in  the  cerebral  hemispheres.     In 

'  If  Pfliiger  had  made  his  experiments  on  decapitated  snakes  he  would  have 
obtained  different  results.  Exner  mentions  that  such  animals  press  their  body 
against  a  fiery  coal  just  as  well  as  against  the  finger  (13). 


I 


CEREBRAL  HEMISPHERES  AND  MEMORY   251 

Invertebrates   they  will    probably   be    found    in  the 
supraoesophageal  ganglion. 

5.  The  spinal-cord-soul  is  not  the  only  instance  in 
which  biologists  have  been  led  astray  by  their  blind 
acceptance  of  metaphysical  notions.  A  second  and 
perhaps  more  general  instance  is  the  assumption  that 
consciousness  exists  in  every  animal  and  is  present  to 
a  certain  degree  even  in  the  ^^^.  Many  authors  ob- 
ject to  the  idea  that  a  thing  like  consciousness  or  the 
soul  should  get  into  the  body  suddenly  at  a  certain 
stage  of  development.  What  they  consider  true  for 
the  ontogenetic  development  they  also  assume  for  the 
phylogenetic  development,  and  they  are  led  to  believe 
that  each  animal  possesses  consciousness.  All  these 
speculations  collapse  as  soon  as  we  free  ourselves 
from  the  influence  of  metaphysics,  and  realise  that 
the  term  consciousness  or  soul  is  applied  by  meta- 
physicians to  phenomena  of  associative  memory,  and 
that  the  latter  depends  upon  a  physical  mechanism 
which  must  be  just  as  definite  as,  for  example,  the 
dioptrical  apparatus  of  our  eye.  I  do  not  think  that 
anybody  maintains  that  every  animal  must  have  an 
apparatus  which  unites  the  rays  of  light  emanating 
from  a  luminous  point  to  an  image  point  on  the  sur- 
face of  its  body,  simply  because  certain  animals  have 
such  an  apparatus.  Moreover,  I  do  not  believe  that 
even  our  biological  metaphysicians  assume  that  this 
dioptrical  apparatus  exists  already  in  the  human  ^<gg, 
and  that  the  latter  is  already  capable  of  visual  space- 
perception,  because  it  would  be  too  awkward  to  as- 


252  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

sume  that  visual  space-perception  should  begin  at  a 
definite  period  of  embryonic  or  post-embryonic  de- 
velopment. And  yet  the  matter  is  in  no  way  different 
for  psychic  phenomena,  if  we  realise  that  what  we  call 
psychic  is  only  a  metaphysical  term  for  functions  of 
associative  memory.  Just  as  our  dioptrical  apparatus 
can  only  begin  to  function  after  the  eye  has  reached 
a  certain  stage  of  development,  the  mechanism  of  as- 
sociative memory  can  only  begin  to  function  after  the 
brain  has  reached  a  certain  stage  of  development. 
And  just  as  only  certain  animals  are  provided  with 
apparatus  for  visual  space-perception,  only  certain  ani- 
mals are  provided  with  the  mechanism  necessary  for 
associative  memory.^  I  think  it  is  time  for  us  to  re- 
alise that  some  of  the  phenomena  of  embryonic  de- 
velopment are  not  continuous  processes  but  decidedly 
discontinuous.  This  is,  of  course,  less  obvious  if  we 
limit  our  study  of  the  organism  to  methods  of  stain- 
ing and  sectioning,  but  it  becomes  very  striking  if 
we  add  some  physiological  methods.  A  pure  \  n 
NaCl  solution  is  extremely  poisonous  to  the  eggs  of 
Fundulus  during  the  first  twelve  hours.  After  that 
it  is  decidedly  less  harmful.  There  is  then  a  discon- 
tinuity in  the  physical  or  chemical  conditions  of  that 
embryo  at  about  twelve  hours  after  fertilisation.  An- 
other discontinuity  is  connected  with  the  beginning 
of  circulation.  Before  circulation  begins  a  f  n  KCl 
solution  is  no  more  harmful  to  the  embryo  of  Fundulus 

^  These  considerations  dispose  also  of  the  conception  of  consciousness  in 
plants  or  of  the  barbarous  notion  of  consciousness  in  molecules  and  atoms. 


CEREBRAL  HEMISPHERES  AND  MEMORY   253 

than  a  f  n  NaCl  solution.  As  soon  as  the  heart  be- 
gins to  beat,  the  KCl  becomes  much  more  poisonous 
than  the  NaCl  solution.  A  similar  discontinuity  is 
noticed  if  we  try  the  effects  of  lack  of  oxygen.  As 
soon  as  the  circulation  begins,  the  Fundulus  embryo 
becomes  quite  suddenly  much  more  sensitive  to  a  lack 
of  oxygen.  The  functional  changes  in  the  embryo 
itself  are  sudden  and  not  gradual  or  continuous.  The 
heart-beat,  for  example,  starts  at  a  certain  time,  sud- 
denly, after  a  certain  stage  of  development  has  been 
reached. 

The  idea  of  a  steady^  continuous  development  is  in- 
consistent with  the  general  physical  qualities  of  proto- 
plasm or  colloidal  material.  The  colloidal  substances 
in  our  protoplasm  possess  critical  points.  If  we  in- 
crease the  pressure  of  a  gas  below  a  certain  tempera- 
ture, at  a  certain  critical  point  the  gas  becomes 
liquid.  The  colloids  change  their  state  very  easily, 
and  a  number  of  conditions  —  temperature,  ions,  en- 
zymes— are  able  to  bring  about  a  change  in  their  state. 
Such  material  lends  itself  very  readily  to  a  discon- 
tinuous series  of  changes,  while  a  gradual  steady 
development,  such  as  most  Darwinians  assume,  is 
practically  excluded. 

We,  of  course,  concede  that  the  associative  memory 
shows  different  degrees  of  development  or  perfection 
in  different  animals.  These  different  degrees  are 
mainly  differences  in  capacity  and  resonance.  By 
difference  in  capacity  I  mean  a  difference  in  the 
number  of  associations  of  which  the  brain  is  capable. 


254  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

By  difference  in  the  resonance  I  mean  the  ease  with 
which  associations  are  produced.  It  is  necessary,  for 
example,  in  the  case  of  a  great  complex  of  sensations, 
that  the  images  of  memory  which  correspond  to  cer- 
tain constituents  of  that  complex  are  easily  repro- 
duced, and  in  the  case  of  a  very  elementary  sensation 
greater  images  of  memory,  which  contain  that  ele- 
mentary sensation  as  a  constituent,  should  be  repro- 
duced. The  quality  of  resonance  is  perhaps  the  more 
important,  as  long  as  the  capacity  does  not  fall  below 
the  average.  The  intelligent  man  differs  from  the 
stupid  man,  among  other  things,  in  the  ease  with  which 
by  means  of  the  associative  memory  he  makes  the 
analysis  or  synthesis  of  the  complexes  of  sensation  : 
that  is,  in  the  slow  or  stupid  man  only  such  images  of 
memory  are  called  up  associatively  as  were  con- 
nected before  with  the  entire  stimulating  complex  ; 
while  in  the  quick  thinker  complexes  of  memory  are 
also  produced  associatively  which  are  connected  with 
single  elements  of  the  stimulating  complex. 

6.  After  what  has  been  said,  it  is  clear  that  the  ab- 
solute mass  of  the  brain  cannot  be  the  principal  factor 
in  determining  intelligence  (lo).  In  different  races 
of  dogs,  for  instance,  the  brain  varies  just  as  much  as 
the  weight  of  the  body.  Dogs  of  a  small  breed  may, 
however,  be  more  intelligent  than  dogs  of  a  large 
breed.  It  also  follows  from  this  that  the  relation  of 
mental  activity  to  the  metabolism  of  the  central 
nervous  system  is  totally  different  from  that  of  mus- 
cular activity  to  the  metabolism  of  the  muscle.     The 


I 


CEREBRAL  HEMISPHERES  AND  MEMORY   255 

power-rate  of  activity  of  the  muscles  is  proportional 
to  their  mass,  and  something  similar  may  be  true  of 
the  glands.  The  results  obtained  by  weighing  the 
brain  of  man  have  proved,  conclusively,  that  the  mass 
of  the  cerebrum,  unless  it  falls  below  a  certain  mini- 
mum, in  no  way  affects  the  degree  of  intelligence. 
The  same  facts  prove  that  the  number  of  ganglion- 
cells  bears  no  direct  relation  to  the  degree  of  intelli- 
gence. The  small  dog  has  fewer  ganglion:cells  than 
the  large  dog,  inasmuch  as  the  size  of  the  cells  varies 
comparatively  little  in  dogs  of  different  size. 

Speck,  who  has  called  attention  to  this  difference 
between  muscles  and  brain  (8),  has  also  made  another 
important  discovery,  namely,  that  in  case  of  lack  of 
oxygen  associative  memory  first  disappears.  He  in- 
haled air  deficient  in  oxygen  from  a  gasometer,  and 
counted  during  his  experiments.  As  soon  as  the 
partial  pressure  of  the  oxygen  of  the  air  fell  below 
8  ^  of  one  atmosphere,  he  forgot  to  count  very  soon 
and  then  fainted,  although  the  other  functions  of  his 
body  showed  no  change.  Speck  concludes  from  this 
that  the  cerebral  hemispheres  are  most  sensitive  to  a 
lack  of  oxygen.  It  is  not  absolutely  necessary  to 
conclude  from  this  that  the  cerebral  hemispheres 
have  relatively  the  greatest  metabolism  of  all  the 
organs.  It  is  possible  that  lack  of  oxygen  affects  the 
physical  qualities  of  colloids  in  the  brain  in  such  a 
way  as  to  make  the  functioning  of  the  mechanisms  of 
associative  memory  impossible.  I  have  shown  that 
lack  of  oxygen  leads  to  a  liquefaction  of  the  cell-walls 


256  COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

in  certain  forms,  and  it  seems  to  be  pretty  generally 
true  that  the  formation  of  solid  cell-walls  becomes 
impossible  under  such  conditions  (n).  It  is  possible 
that  in  the  case  of  lack  of  oxygen,  physical  changes 
in  the  state  of  certain  constituents  of  the  brain  are 
prevented  which  are  necessary  for  the  activity  of 
memory. 

Some  physiologists  seem  to  be  of  the  opinion  that 
when  the  brain  contains  a  good  deal  of  blood  the 
body  has  a  special  feeling  of  happiness.  I  recall  a 
popular  lecture  by  a  prominent  psychiatrist  in  which 
he  maintains  that  when  the  cerebral  hemispheres  con- 
tain a  great  deal  of  blood  the  proprietor  of  this  brain 
enjoys  the  absolute  happiness  (?)  of  an  intoxication 
from  champagne.  This  psychiatrist  evidently  ima- 
gines that  the  greater  the  supply  of  blood  is,  the 
better  the  brain  is  nourished,  and  that  with  the  in- 
creasing nourishment  of  the  brain  the  feeling  of 
happiness  increases.  Among  the  food-substances 
which  are  offered  to  the  brain  in  large  quantities  by 
the  dilatation  of  the  arteries  oxygen  takes  the  first 
place.  It  was  formerly  assumed  that  the  oxygen- 
supply  determined  the  metabolism,  but  we  now  know 
definitely  that  internal  processes  in  the  tissues 
determine  the  consumption  of  oxygen,  probably 
processes  of  fermentation.  If  a  certain  quantity  of 
oxygen  is  present  in  the  brain,  the  superfluous  oxygen 
has  no  effect.  The  same  is  probably  true  of  all  the 
other  food-constituents.  Under  normal  conditions 
the  oxygen-supply  in  the  brain  is  sufificient  as  long  as 


CEREBRAL  HEMISPHERES  AND  MEMORY  257 

the  circulation  is  normal.  It  harmonises  with  these 
facts  that  mental  activity  does  not  influence  the 
phenomena  of  oxidation,  as  Speck  has  proved  by  very 
careful  experiments.  But  from  this  we  must  not  con- 
clude that  the  activity  of  the  brain  takes  place  with- 
out chemical  changes,  only  that  the  chemical  changes 
which  are  determined  by  mental  activity  are  too 
slight  to  be  recognised.  The  statement  that  dilatation 
of  the  blood-vessels  of  the  brain  produces  a  sensation 
of  happiness  is  not  based  upon  any  fact  that  has 
been  proved  scientifically. 

7.  The  amoeboid  changes  in  the  ganglion-cells  have 
been  utilised  to  account  for  the  phenomena  of  asso- 
ciation. As  far  as  normal  processes  of  association 
are  concerned,  these  amoeboid  changes  cannot  play 
any  r6le,  as  they  are  much  too  slow.  We  notice 
migrations  of  the  cones  and  the  pigment  in  the 
retina,  yet  the  idea  that  these  protoplasmic  motions 
play  any  rdle  for  space-  or  colour-perception  has  to 
be  abandoned  for  the  same  reason. 

Other  authors  hold  that  conditions  of  incomplete 
association,  as  in  the  case  of  dreams,  or  interruption 
of  association,  as  in  the  case  of  deep  sleep  or 
narcotics,  are  due  to  a  partial  or  complete  discon- 
nection of  the  ganglion-cells  by  a  shortening  of  the 
processes.  It  does  not  seem  to  me  that  the  obser- 
vations which  we  thus  far  possess  prove  anything  of 
that  character  (9,  12). 


258    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

Bibliography. 

1.  SCHRADER,  Max  E.  G.  Zur  Physiologie  des  Froschhirns. 
P finger's  Archiv,  Bd.  xli.,  1887. 

2.  ScHRADER.  Die  Stellung  des  Grosshirns  im  Reflextnechan- 
ismus.  Archiv  fur  experiment.  Pathologie  und  Pharmakologiey 
Bd.  xxix.,  1892. 

3.  GoLTZ,  F.  Beitrdge  zur  Lehre  von  den  Nervencentren  des 
Frosches.     Berlin,  1868. 

4.  ScHRADER,  Max  E.  G.  Zur  Physiologie  des  Vogelgehirns. 
Pfiugers  Archiv,  Bd.  xliv.,  1889. 

5.  Steiner,  J.  Die  Funciionen  des  Centralnervensy stems  und 
ihre  Phylogenese.     II.  Abth.  :  Die  Fische.     Braunschweig,  1885. 

6.  GoLTZ.  F.  Der  Hund  ohne  Grosshirn.  Pfliiger's  Archiv , 
Bd.  li.,  1892. 

7.  Pfluger,  E.  Die  sensorischen  Functionen  des  Rilckenmarks. 
Berlin,  1853. 

8.  Speck.  Physiologie  des  menschlichen  Athmens.  Leipzig, 
1892. 

9.  Duval,  M.  Thiorie  histologique  du  sommeil.  C.  R.  Soc.  de 
Biol.,  1895. 

10.  Donaldson,  H.  H.      The  Growth  of  the  Brain.     London, 

1895- 

11.  LoEB,  J.  Untersuchungen  Uber  die  physiologischen  Wir- 
kungen  des  Sauer  staff  mangels.     Pfiiiger's  Archiv,  vol.  Ixii.,  1895. 

12.  Bawden,  H.  H.  a  Digest  and  a  Ci'iticism  of  the  Data 
upon  which  is  Based  the  Theory  of  Amoeboid  Movements  of  the 
Neuron.      The  Journal  of  Comparative  Neurology,  vol.  x.,  1900. 

13.  ExNER,  S.  Entwurf  zu  einer  physiologischen  Erkldrung  der 
psychischen  Erscheinungen,     Leipzig  and  Wien,  1894,  p.  85. 


CHAPTER   XVII 

ANATOMICAL  AND  PSYCHIC  LOCALISATION 

I.  It  follows  from  the  facts  of  the  preceding  chap- 
ter that  the  cerebral  hemispheres  are  a  necessary 
organ  for  the  phenomena  of  associative  memory. 
We  are  not  quite  justified  in  saying  that  they  are  the 
specific  organ  for  this  function.  It  may  be  possible, 
although  not  probable,  that  other  parts  of  the  brain 
are  also  required  for  this  purpose.  It  is  certain  that 
the  spinal  cord  is  not  needed  for  this  function,  for 
animals  whose  spinal  cord  is  severed,  or  from  whom 
the  greater  part  of  it  has  been  removed,  show  no  de- 
ficiency in  the  process  of  associative  memory. 

The  cerebral  hemispheres  form  an  appendage  of 
the  segmental  central  nervous  system.  They  are  con- 
nected with  at  least  some  of  the  segmental  ganglia  by 
special  nerve-fibres.  As  these  different  bundles  of 
fibres  enter  the  cortex  at  different  places,  it  is  obvious 
that  if  we  stimulate  the  various  spots  of  the  surface  of 
the  cortex  with  electric  currents  of  the  smallest  in- 
tensity necessary  to  produce  a  reaction,  we  must 
notice  different  effects.  If,  for  instance,  a  current  of 
minimal  intensity  be  sent  through  the  spot  D  (Fig. 

259 


26o    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 


39),  where  the  fibres  from  and  to  the  brachial  segment 
of  the  cord  of  a  dog  enter  the  cortex,  contractions  of 

certain  muscles  of  the  fore- 
leg must  follow.  If  we 
stimulate  the  region  A  (Fig. 
39),  which  is  connected  with 
the  sensory  or  motor  ganglia 
of  the  eyes,  motions  of  the 
latter  must  be  produced.  It 
is,  moreover,  evident  that  if 
we  injure  the  spot  D  in  the 
cortex  we  must  get  some- 
what different  after-effects 
from  those  produced  when 
A  is  injured.  In  the  former 
case  we  must  expect  motor 
disturbances  in   the  use  of 

Fig.  39.  Cerebral  Hemispheres    the  fore-leg,  in  the  latter  dis- 
OF  A  Dog.  ^      ,  r     •   • 

A,  optical  region;  D,  brachial  region;       tUrbaUCeS   of  VlSlOn. 
G,  region  of  the  hind-leg.      (After  J|-      jg       q£     cOUrSe,      nOt     tO 

Munk.)  '  '  ^  ^ 

be  expected  that  the  distri- 
bution of  segmental  fibres  on  the  cortex  follows  min- 
utely the  arrangement  of  the  ganglia  in  the  spinal 
cord.  Displacements  of  elements  occur  in  the  cerebral 
hemispheres  during  the  process  of  growth.  This  is 
indicated  by  the  formation  of  folds  formed  on  the 
surface.  It  is  possible  that  not  all  the  segmental 
ganglia  send  fibres  directly  to  the  hemispheres,  and  it 
is  possible  that  certain  ganglia  are  connected  with  the 
cortex  at  more  than  one  spot  or  region.     From  the 


ANATOMICAL  AND  PSYCHIC  LOCALISATION    261 

fact  that  the  different  bundles  of  fibres  from  the  vari- 
ous segmental  ganglia  enter  at  different  spots  in  the 
cortex,  some  authors  have  drawn  the  conclusion  that 
there  is  not  only  an  anatomical  localisation  of  fibres ^ 
but  also  a  psychic  localisation  of  functions.  They 
assume  that  the  various  psychic  functions  take  place 
in  different  regions  of  the  cortex.  The  occipital 
region,  where  the  fibres  from  the  segmental  ganglia 
of  the  optic  nerve  enter,  is  considered  by  these  authors 
as  the  seat  of  visual  consciousness.  At  the  spot  D 
(where  the  brachial  fibres  enter  or  leave)  the  "  con- 
sciousness of  the  fore-leg"  is  said  to  be  localised. 
These  assumptions  are  contradicted  by  the  plain  facts 
of  associative  memory.  Simultaneous  processes  in 
different  sense-organs  are  fused  in  our  memory.  The 
odour  of  a  rose  recalls  its  visual  image.  This  could 
not  be  possible  if  the  visual  processes  were  confined 
to  one  region  of  the  cerebral  hemispheres  ;  they  must 
spread  to  the  olfactory  region,  and  vice  versa.  The 
same  can  be  said  of  other  kinds  of  stimulation  and  of 
combinations  of  more  than  two  stimuli.  Moreover, 
we  remember  not  only  simultaneous  sense-impressions, 
but  we  remember  a  whole  series  dependent  upon  suc- 
cessive stimuli  of  different  character,  if  only  the  first 
constituent  of  such  a  series  has  been  aroused.  This 
indicates  that  even  the  after-effects  of  a  stimulus  must 
spread  all  over  the  cerebral  hemispheres,  so  that  they 
may  fuse  with  the  successive  processes  going  on  in 
the  brain.  It  is  thus  obvious  that  the  assumption  of 
a  localisation  of  psychic  functions  in  the  cortex  is 


/ 


262   COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

opposed  to  the  elementary  facts  of  associative  memory 
or  consciousness. 

2.  Experiments  on  the  brain  indicate  that  while 
there  exists  to  a  certain  extent  an  anatomical  localisa- 
tion in  the  cortex,  the  assumption  of  a  psychical 
localisation  is  contradicted  by  the  facts.  The  occipi- 
tal region  of  the  cerebral  hemispheres  is  said  to  be 
the  seat  of  visual  processes,  the  temporal  lobes  the 
seat  of  auditory  processes.  If  the  occipital  regions 
are  removed,  only  the  visual  processes  are  said  to 
cease,  while  if  the  temporal  regions  are  removed,  only 
the  auditory  processes  are  said  to  disappear.  We 
know  that  persons  who  were  born  blind  and  deaf  have 
shown  a  normal  or  even  a  superior  intellect  (Laura 
Bridgman).  If  the  theory  of  psychic  localisation 
were  correct,  we  should  expect  that  an  animal  from 
whose  hemispheres  the  occipital  and  temporal  regions 
are  removed  would  become  blind  and  deaf,  but  would 
remain  normal  in  other  directions.  But  Goltz  has 
shown  that  such  an  animal  (dog)  becomes  hopelessly 
idiotic  (2,  v.).  The  processes  of  association  even  of  the 
other  senses  are  no  longer  normal.  This  agrees  with 
the  idea  that  in  processes  of  association  the  cerebral 
hemispheres  act  as  a  whole,  and  not  as  a  mosaic  of  a 
number  of  independent  parts. 

Goltz  has  proved  that  if  we  remove  one  whole 
hemisphere  in  a  dog  the  personality  of  the  animal  or, 
in  other  words,  the  sum-total  of  its  associations  remains 
the  same.  The  dog  recognises  its  friends  and  all  the 
other  objects  it  has  ever  known,  and  it  reacts  in  such 


ANATOMICAL  AND  PSYCHIC  LOCALISATION    263 

a  way  as  to  indicate  that  its  associative  memory  has 
not  suffered  through  the  operation.  But  if  the  an- 
terior parts  of  both  hemispheres  be  removed,  the  dog 
is  no  longer  normal,  but  idiotic.  It  no  longer  reacts 
in  the  same  way  it  did  before,  and  it  is  obvious  that 
its  associative  memory  has  suffered.  The  same  is  true 
if  both  posterior  halves  of  the  cerebral  hemispheres  be 
removed  (2,  V.). 

If  we  ask  at  present  what  determines  this  difference, 
we  are  at  a  loss  to  give  an  answer.  We  might  point 
out  that  the  right  and  left  hemispheres  are  practically 
symmetrical,  while  the  anterior  and  posterior  parts 
are  not  symmetrical.  If  the  form  or  orientation  of 
the  elements  be  of  importance,  we  might  conceive  of 
the  possibility  that  in  a  brain  with  only  one  cerebral 
hemisphere  all  the  processes  could  occur  in  approxi- 
mately the  same  form,  while  in  the  brain  with  both 
posterior  or  both  anterior  halves  of  the  hemispheres 
gone,  the  processes  of  association  could  not  be  re- 
peated in  the  same,  but  in  a  mutilated  form.  Hence 
the  idiocy  which  follows  such  operations.  We  might 
illustrate  this  by  an  analogous  experience  in  the  phy- 
siology of  sound.  Each  vowel  is  determined  by  a 
sound  of  a  certain  pitch.  If  a  singer  sings  in  a  pitch 
higher  than  that  of  the  determinant,  the  vowel  becomes 
indistinct.  It  is  possible  that  in  the  brains  of  the 
above-mentioned  dogs  the  associations  are  rendered 
impossible  or  difficult,  because  certain  elemental  pro- 
cesses are  no  longer  possible. 

3.   In  this  connection  I  may  mention  that  the  bo- 


264    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

servations  of  Goltz  indicate  a  connection  of  the  main 
regions  of  the  cerebral  hemispheres  with  certain 
regions  in  the  medulla  oblongata.  A  dog  that  has 
lost  the  anterior  halves  of  both  cerebral  hemispheres 
has  a  tendency  to  run  with  its  head  bent  down.  A 
dog  which  has  lost  the  posterior  halves  of  both  hemi- 
spheres shows  the  opposite  tendency.  It  moves  very 
little  and  its  head  is  carried  high  in  the  air.  Its  an- 
terior legs  are  stiff  and  often  stretched  forward.  The 
difference  in  the  position  and  progressive  motions  of 
these  two  animals  seems  to  be  somewhat  similar  to  the 
difference  in  the  attitude  of  an  Amblystoma  when 
stimulated  by  constant  currents.  The  position  of 
the  dog  in  which  the  anterior  halves  of  the  cerebral 
hemispheres  are  removed  resembles  that  of  an  Am- 
blystoma in  a  descending  current,  while  the  attitude 
of  the  dog  without  the  occipital  halves  of  the  hemi- 
spheres is  like  that  of  an  Amblystoma  in  an  ascending 
current.  (See  Chapter  XI.)  If  in  a  dog  one  cerebral 
hemisphere  be  removed,  while  the  other  is  intact,  the 
dog  makes  circus-motions  toward  the  injured  side. 
There  is  an  unmistakable  analogy  between  these  ob- 
servations and  the  older  experiments  of  Magendie 
and  Flourens  on  the  sectioning  of  the  crura  cerebelli. 
While  dogs  after  the  loss  of  the  anterior  halves  of 
the  cerebral  hemispheres  often  become  irritable  and 
ugly,  dogs  which  lose  the  occipital  halves  of  both 
hemispheres  invariably  become  good-natured  and 
harmless.  This  indicates  a  connection  of  the  cerebral 
hemispheres  with  organs  of  the  body  for  which  with 


ANATOMICAL  AND  PSYCHIC  LOCALISATION    265 

our  present  knowledge  of  anatomical  localisation  we 
cannot  yet  account. 

4.  Those  who  believe  in  a  psychic  localisation  in 
the  cerebral  hemispheres  base  their  claims  chiefly  on 
the  effects  of  small  lesions.  If  our  point  of  view  is 
correct,  we  should  expect  that  small  lesions  either 
make  no  noticeable  functional  disturbance  at  all,  or 
cause  disturbances  which  are  no  more  psychic  than 
those  following  the  cutting  of  a  peripheral  nerve. 
Hitzig  and  Fritsch  were  the  first  to  destroy  the  cortex 
of  the  centre  of  the  fore-leg  (D,  Fig.  39)  in  one  of 
the  hemispheres  of  a  dog  (i).  When  this  centre  was 
destroyed  in  the  left  hemisphere,  the  right  leg  showed 
the  following  disturbance  :  **  In  running,  the  animals 
did  not  use  the  right  fore-paw  to  advantage.  It  was 
turned  in  or  out  too  much  and  did  not  furnish  a  proper 
support.  This  never  happened  with  the  other  paws. 
Movement  did  not  fail  entirely,  but  in  the  right  leg  the 
movement  of  adduction  was  somewhat  weaker.  In 
standing,  the  dorsal  side  of  the  paw  was  often  used  in- 
stead of  the  sole  "  (i)-  ^^  ^he  paw  was  placed  in  abnor- 
mal positions,  no  attention  was  paid  to  it  by  the  dog. 
Hitzig  and  Fritsch  draw  the  following  conclusions  from 
these  observations  :  "  The  animals  evidently  had  only 
an  imperfect  consciotisness  of  the  condition  of  this  limb  ; 
ihey  had  lost  the  ability  to  form  perfect  ideas  concern- 
ing ity  In  the  opinion  of  Hitzig  we  have  to  deal 
with  a  psychical  disturbance,  or,  as  we  should  say,  a 
disturbance  of  associative  memory.  This  disturbance 
of  associative  memory  is,  however,  confined  to  such 


266    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

processes  as  involve  the  right  fore-leg.  In  our  opinion, 
the  phenomena  observed  by  Hitzig  are  the  outcome  of 
a  weakening  of  certain  groups  of  muscles  and  a  diminu- 
tion of  the  sensibility  in  the  right  leg.  Such  disturb- 
ances could  just  as  well  be  produced  by  a  pressure 
upon  certain  peripheral  nerve-fibres. 

That  Hitzig's  psychological  interpretation  of  his 
observation  is  wrong  has  been  proved  by  Goltz.  If 
Hitzig's  idea  were  correct,  we  ought  to  assume  that,  if 
the  centre  of  the  right  fore-leg  were  removed,  a  dog 
should  no  longer  be  able  to  use  the  right  paw  as  a 
hand,  where  such  a  use  is  based  upon  the  activity  of 
associative  memory.  Goltz  not  only  removed  the 
centre  but  the  entire  left  hemisphere  of  a  dog  that 
had  been  taught  to  dig  its  food  out  of  a  heap  of 
pebbles.  This  dog  showed  all  the  disturbances  of 
the  right  leg  which  Hitzig  described.  Yet  it  con- 
tinued to  dig  its  food  (pieces  of  meat)  out  of  the 
heap  of  pebbles  with  the  right  fore-paw.  It  preferred 
to  use  the  left  paw  for  this  purpose.  But  when  this 
was  forbidden  it  used  the  right  paw  with  success. 
This  experiment  proves  that  the  conscious  or  psy- 
chical character  of  the  motions  of  the  fore-leg  is  not 
affected  by  the  removal  of  its  cortical  centre.  A  close 
observation  of  the  way  the  dog  uses  this  paw  shows 
that  certain  muscle-groups  must  have  suffered  by 
the  operation,  and  a  closer  analysis  of  these  purely 
muscular  disturbances  explains  the  anomalies  which 
Hitzig  had  mistaken  to  be  of  a  psychical  character. 
Removal  of  the  fore-leg  centre  causes  a  decrease  in 


ANA  TOMICAL  AND  PSYCHIC  LOCALISA  TION    267 

the  tension  of  the  extensors  of  the  leg  (and  perhaps 
also  of  other  groups  of  muscles).  For  this  reason 
the  leg  slips  easily  and  bends  in  the  ankle-joint  so  that 
the  animal  sometimes  steps  on  the  back  instead  of  the 
sole  of  the  foot.  It  does  not  notice  if  the  leg  is 
placed  in  an  abnormal  position.  This  is  partly  due  to 
the  diminution  in  resistance  caused  by  the  weakening 
of  certain  muscles  and  partly  due  to  a  reduction  in  the 
sensibility  of  the  skin.  Goltz  has  proved  that  it  re- 
quires a  greater  pressure  on  the  skin  of  this  leg  to 
cause  the  dog  to  withdraw  it  than  on  any  of  the  other 
legs.  This  explains  also  why  the  dog  does  not  notice 
if  the  foot  whose  cortical  centre  has  been  removed  is 
placed  in  cold  water.  There  are,  then,  changes  in  the 
tension  of  certain  muscles  and  a  reduction  in  the 
sensibility  of  the  skin  which  suffice  to  explain  all 
the  disturbances  observed  by  Hitzig,  but  there  is  no 
loss  of  muscular  ''consciousness"  as  Hitzig  assumes. 
To  a  certain  extent,  similar  effects  can  be  produced  by 
dividing  the  posterior  roots  of  the  arm-nerves.  It 
would  hardly  occur  to  anyone  to  maintain  for  this 
reason  that  the  psychic  centre  of  the  arm-movements 
is  localised  in  the  posterior  roots.  Further  proof  that 
these  disturbances  described  by  Hitzig  are  due  to  a 
decrease  in  the  tension  of  the  extensors  is  furnished 
by  the  fact  that  in  man,  when  an  arm  becomes  para- 
lysed after  a  local  disease  in  the  cerebral  hemispheres, 
a  contraction  producing  a  flexed  position  of  the  arm 
takes  place  after  a  time.  Not  all  the  muscles  of  the 
arm  are  completely  paralysed  as  a  result  of  the  disease 


268    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

in  the  hemispheres  ;  but  the  tension  of  the  extensors 
has  decreased,  and  as  a  result  the  tension  of  the  flexors 
alone  determines  the  position  of  the  arm. 

In  Goltz's  experiment  the  centre  of  the  right  fore- 
leg alone  had  been  removed.  It  has  been  said  that 
the  centre  of  the  left  fore-leg  situated  in  the  other 
hemisphere  performed  the  psychic  functions  for  both 
legs  after  the  operation.  I  made  an  experiment  to 
which  this  objection  is  not  possible.  A  dog  was 
taught  to  walk  on  its  hind-legs  when  it  wanted  to  be 
fed.  Then  the  hind-leg  centres  were  removed  (G,  Fig. 
39)  in  both  hemispheres.  In  spite  of  this  loss  the 
dog  was  still  able  to  walk  on  its  hind-legs.  When- 
ever I  offered  it  food  or  whenever  it  expected  to  be 
fed  it  rose  voluntarily  on  its  hind-feet.  The  conscious 
actions  or  associatio7ts  for  the  use  of  the  hind-legs  had 
not  suffered,  but  there  was  decidedly  a  muscular  dis- 
turbance inasmuch  as  the  dog  was  not  able  to  stand 
so  long  on  its  hind-legs  as  it  could  before  the  opera- 
tion. I  showed  this  dog  at  the  naturalists'  meeting  in 
Berlin  in  1886.  The  day  after  the  demonstration  I 
showed  the  brain  of  the  animal  that  had  been  killed 
in  the  meantime.  The  hind-leg  centres  had  been 
removed  completely. 

It  must,  however,  be  explicitly  stated  that  not  every 
limited  lesion  in  the  motor  centres  leads  to  a  disturb- 
ance. This  is  not  only  of  importance  from  a  theoretical 
but  also  from  a  practical  point  of  view.  A  physician 
need  not  be  surprised  if  a  post-mortem  examination 
shows  a  circumscribed  lesion  in  the  cortex  which  had 


ANATOMICAL  AND  PSYCHIC  LOCALISATION    269 

not  caused  any  clinical  symptoms.  It  is  obvious  that 
certain  organs  are  more  easily  disturbed  by  a  lesion 
in  the  cortex  than  others.  An  operation  in  the  centre 
of  the  fore-leg  produces  disturbances  more  easily  than 
an  operation  in  the  centre  of  the  hind-leg.  There 
are  certain  parts  of  the  body  in  which  no  disturbances 
can  be  produced  by  the  extirpation  of  their  so-called 
centres  in  the  cortex.  Nobody  has  thus  far  been  able 
to  produce  a  paresis  or  paralysis  of  the  upper  eyelid 
in  a  dog  or  to  produce  loss  of  sensibility  in  the  cornea 
by  an  operation  in  the  cortex.  It  must,  moreover, 
not  be  overlooked  that  all  the  disturbances  which 
follow  small  lesions  of  the  cortex  in  dogs  are  only 
transitory. 

5.  Not  only  the  motor  but  also  the  sensory  disturb- 
ances which  follow  an  operation  in  the  cerebral 
hemispheres  have  been  interpreted  as  psychic  dis- 
turbances. We  know  that  a  lesion  of  the  surface  of 
the  occipital  lobes  causes  visual  disturbances.  Munk 
has  interpreted  these  disturbances  which  follow  a 
small  lesion  of  one  of  the  visual  spheres  as  psychic 
(4).  There  is  a  small  region  (Aj  Fig.  39)  in  each  of 
the  occipital  lobes  the  destruction  of  which,  according 
to  Munk,  causes  a  psychic  blindness  in  the  opposite 
eye.  By  psychic  blindness  Munk  means  the  fact  that 
the  dog  does  not  recognise  what  it  sees,  although  it  is 
by  no  means  blind.  If  the  cortex  be  removed  at  the 
region  A,  in  the  left  hemisphere,  the  dog  shows  psychic 
blindness  in  the  right  eye.  Such  a  dog,  for  instance, 
is  no  longer  afraid  of  a  burning  match  or  of  the  whip. 


270    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

provided  its  left  eye  be  closed.  Munk  assumes  that 
the  image  of  memory  of  the  whip  or  the  burning 
match  had  been  deposited  in  the  region  Aj  and  was 
lost  with  the  loss  of  this  place.  It  can  be  shown  that 
Munk  is  as  much  mistaken  concerning  the  psychic 
character  of  the  visual  disturbance  following  the  de- 
struction of  a  small  region  in  the  occipital  lobes,  as 
Hitzig  was  in  regard  to  the  psychic  character  of  the 
motor  disturbances  following  the  destruction  of  a 
centre  of  the  fore-leg.  In  the  majority  of  cases  the 
removal  of  the  region  A  ^  in  one  hemisphere  produces 
no  visual  disturbance.  In  the  cases  where  a  visual 
disturbance  is  produced  it  is  only  temporary.  I 
noticed  indeed  that  such  dogs  may  no  longer  recog- 
nise objects  in  the  opposite  eye,  but  the  reason  for 
this  is  altogether  different  from  that  assumed  by 
Munk. 

It  is  known  that  in  man  the  destruction  of  the 
visual  sphere  in  one  hemisphere  causes  the  same  dis- 
turbance as  the  destruction  of  the  optic  tract  of  the 
same  side — namely,  a  hemianopia  of  the  opposite  half 
of  the  visual  field.  This  disturbance  is  not  psychic 
but  purely  physiological,  inasmuch  as  it  results  in 
a  loss  of  irritability  on  one  side  of  each  retina,  but  not 
in  a  loss  in  the  processes  of  association.  The  same 
occurs  in  a  dog  whose  visual  sphere  has  been  injured 
in  one  spot,  with  this  difference,  however,  that  the 
loss  of  irritability  is  not  complete.  Thus  if  the  left 
occipital  region  be  injured  in  a  man,  a  hemianopia  of 
the  left  sides  of  both  retinae  follows,  and  the  patient 


ANATOMICAL  AND  PSYCHIC  LOCALISATION    271 

sees  nothing  in  the  right  half  of  his  visual  field.  If 
the  same  operation  be  performed  in  a  dog,  it  causes 
not  a  complete  hemianopia  but  a  hemiamblyopia  (5). 
The  dog  is  not  blind  for  the  right  half  of  its  visual 
field,  but  has  only  a  reduced  power  of  vision.  It  be- 
haves like  an  animal  that  pays  less  attention  to  that 
half  of  its  visual  field,  or  whose  threshold  for  this  half 
is  reduced.  If  we  stand  before  such  a  dog  and  hold 
two  pieces  of  meat  in  front  of  it,  simultaneously,  one 
piece  in  each  hand,  the  dog  invariably  chooses  the 
piece  at  its  left.  It  almost  seems  as  though  it  did 
not  see  the  piece  at  the  right.  Now  we  know  that  a 
moving  object  acts  as  a  stronger  optical  stimulus  than 
a  stationary  object.  If  the  two  pieces  of  meat  are 
again  held  before  the  dog  in  the  manner  described 
above,  only  with  the  difference  that  the  piece  that  is 
in  the  right  half  of  the  field  of  vision  is  moved,  the  dog 
jumps  at  the  latter  (6).  This  proves  that  in  the  dog 
the  threshold  of  stimulation  for  optical  stimuli  has 
been  raised  in  the  right  half  of  the  field  of  vision. 
But  how  could  Munk  mistake  the  hemiamblyopia  for 
a  psychic  disturbance?  In  a  dog,  the  divergence  of 
the  optical  axes  is  greater  than  in  man.  Hence  the 
right  half  of  the  visual  field  is  controlled  more  by  the 
right  eye  than  by  the  left.  If  we  produce  the  hemi- 
amblyopia or  the  hemianopia  in  a  dog,  the  eye  oppo- 
site the  injured  hemisphere  is  blind  or  injured  for 
considerably  more  than  one  half  of  its  retina.  If  the 
other  eye  of  such  a  dog  be  closed,  its  field  of  vision  is 
reduced  to  a  very  small  area,  and  the  dog  does  not 


272    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

recognise  the  objects,  although  It  is  not  entirely  blind. 
What  Munk  mistook  for  psychic  blindness  is,  in  real- 
ity, only  hemiamblyopia  or  hemianopia  (5,  6). 

6.  One  of  the  main  arguments  which  Munk  used 
for  his  assumption  of  a  psychic  character  of  the  visual 
disturbances  caused  by  the  effects  of  a  unilateral  lesion 
of  a  visual  sphere  was  the  fact  that  these  disturbances 
disappear  in  about  six  weeks.  On  the  basis  of  this 
fact  he  constructed  the  following  hypothesis  :  The 
visual  images  of  memory  are  deposited  each  in  a 
single  ganglion-cell  or  a  group  of  cells  in  the  region 
A^  of  the  opposite  hemisphere.  If  this  region  be  re- 
moved, the  dog  loses  all  its  images  of  memory.  But 
new  images  of  memory  can  be  deposited  in  the  sur- 
rounding parts  A.  This  will  be  done  after  the  loss  of 
the  region  Aj  and  the  dog  becomes  normal  again  after 
six  weeks.  If  this  hypothesis  of  Munk  were  correct, 
visual  disturbances  of  such  a  dog  should  not  disap- 
pear if  it  were  kept  in  the  dark,  where  it  would  have 
no  chance  to  acquire  new  visual  images  of  memory. 
I  made  that  experiment.  In  dogs  which  possessed 
only  the  right  eye,  the  region  Aj  in  the  left  cerebral 
hemisphere  was  destroyed.  In  the  majority  of  these 
dogs,  the  operation  produced  no  effect.  In  a  few, 
hemiamblyopia  occurred.  Of  these  several  were  put 
in  an  absolutely  dark  room  for  the  following  six  weeks. 
As  soon  as  they  were  taken  out  they  were  entirely 
normal.  This  proves  that  their  recovery  was  not  due 
to  the  acquisition  of  new  visual  images  of  memory, 
but  to  the  fact  that  a  purely  physiological  effect  upon 


ANATOMICAL  AND  PSYCHIC  LOCALISATION    273 

the  irritability  of  the  optical  apparatus  caused  by  the 
operation  wears  off  after  a  certain  time. 

We  then  come  to  the  conclusion  that  the  apparent 
psychic  blindness  which  follows  the  destruction  of  the 
region  Aj  in  the  opposite  hemisphere  is  exclusively  a 
hemianopia  or  hemiamblyopia.  This  disturbance  is 
no  psychic  disturbance  inasmuch  as  it  can  be  pro- 
duced by  an  injury  to  a  peripheral  nerve,  the  optic 
tract. 

7.  We  must  seek  an  explanation  for  the  temporary 
character  of  the  disturbance  which  follows  small 
lesions.  If  the  lesion  covers  a  large  area,  the  dis- 
turbance is  more  permanent.  Goltz  assumes  that 
these  transitory  effects  are  shock-effects  due  to  the 
operation.  He  was  led  to  this  assumption  through 
his  experiments  on  the  spinal  cord.  If  the  spinal  cord 
be  cut  in  a  dog,  no  segmental  reflexes  occur  during 
the  first  days  or  weeks  after  the  operation  in  the  part 
of  the  animal  below  the  cut.  "  Pressing  on  the  hind- 
feet  produces  no  reaction.  In  the  male  dog,  erection 
of  the  penis  cannot  be  aroused  reflexly.  The  urine 
collects  in  the  relaxed  bladder.  The  anus  gaps.  In 
brief,  the  whole  posterior  part  of  the  body  seems  un- 
irritable.  A  few  days  later  the  apparently  dead  spi- 
nal cord  may  have  recovered  almost  entirely.  The 
posterior  part  of  the  animal  then  offers  a  large  num- 
ber of  reflex  phenomena.  No  one  will  assume  that 
that  piece  of  the  spinal  cord  which  is  separated  from 
the  brain  in  so  short  a  time  acquires  entirely  new 

powers  as  a  reflex  organ  ;  we  must  assume  that  these 
18 


274    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

powers  were  only  suppressed  or  inhibited  temporarily 
by  the  lesion  of  the  spinal  cord."  The  same  is  true 
in  regard  to  the  vasomotors.  Division  of  the  spinal 
cord  reduces  the  tonus  of  the  blood-vessels  of  the 
posterior  legs.  After  a  time  the  blood-vessels  recover 
and  become  normal  again.  Now  if  the  sciatic  nerve 
in  the  same  animal  be  severed,  a  new  temporary  para- 
lysis of  the  vasomotors  follows.  This  proves  that 
the  vasomotor  paralysis  in  the  hind-legs  that  occurs 
after  the  division  of  the  spinal  cord  is  due  to  a 
shock-effect  of  the  operation.  What  the  nature  of 
this  shock-effect  is  we  do  not  know.  Perhaps  v. 
Cyon's  experiment  throws  light  on  this :  v.  Cyon 
showed,  namely,  that  the  tension  of  the  muscles  de- 
creases after  the  division  of  the  posterior  root  of  their 
segment  (3). 

8.  We  conclude  from  all  these  observations  on  dogs 
that  small  lesions  do  not  cause  any  disturbances  in  the 
processes  of  associative  memory,  and  that  Hitzig  and 
Munk  are  wrong  in  interpreting  the  disturbances  fol- 
lowing the  excision  of  a  small  piece  of  the  cortex  as 
psychic  disturbances.  In  the  majority  of  cases  such 
slight  lesions  cause  no  disturbance,  and  where  any 
is  caused  it  is  of  such  a  character  as  could  be  pro- 
duced by  the  lesion  of  a  peripheral  nerve.  If  we  wish 
to  produce  psychic  disturbances  by  a  lesion  of  the 
brain,  we  must  destroy  extensive  parts  of  both  hemi- 
spheres. Operations  in  one  hemisphere  alone,  and 
even  the  destruction  of  an  entire  hemisphere,  have  no 
such  effect. 


ANATOMICAL  AND  PSYCHIC  LOCALISATION    275 

It  has  been  claimed  that  the  intellect  is  the  func- 
tion of  special  parts  of  the  brain.  Hitzig  and  others 
assumed  that  the  frontal  lobes  of  the  cerebral  hemi- 
spheres are  the  organs  of  attention.  I  have  repeat- 
edly removed  both  frontal  lobes  in  dogs  (6).  It  was 
impossible  to  notice  the  slightest  difference  in  the 
mental  functions  of  the  dog.  There  is  perhaps  no 
operation  which  is  so  harmless  for  a  dog  as  the  re- 
moval of  the  frontal  lobes.  Flechsig  thinks  that  it  is 
not  only  the  frontal  lobe  but  the  cortex  of  certain 
other  regions  which  is  responsible  for  mental  activity, 
inasmuch  as  it  is  the  seat  of  "centres  of  association." 
I  have  removed  the  cortex  of  Flechsig's  **  centres  of 
association  "  in  dogs  without  having  noticed  anything 
that  justifies  Flechsig's  hypothesis.  The  assumption 
of  "  centres  of  association"  is  just  as  erroneous  as  the 
assumption  of  a  centre  of  coordination  in  the  heart. 
Association  is,  like  coordination,  a  dynamical  effect 
determined  by  the  conductivity  of  the  protoplasm. 
Associative  processes  occur  everywhere  in  the  hemi- 
spheres (and  possibly  in  other  parts  of  the  brain),  just 
as  coordination  occurs  wherever  the  connection  be- 
tween two  protoplasmic  pieces  is  sufficient.  It  is  just 
as  anthropomorphic  to  invent  special  centres  of  associ- 
ation as  it  is  to  invent  special  centres  of  coordination. 

Bibliography. 

1.  Hitzig,  E.  Uniersuchungen  ilber  das  Gehirtiy  Berlin,  1874  ; 
and  Reicherfs  und  Du  Bois-Reymond's  ArchiVy  1870. 

2.  GoLTZ,  F.     Ueber  die  Verrichtungen  des  Grosshirns. 


it 

(( 

{( 

u 

xiv.,  1877. 

u 

« 

it 

ii 

XX.,  1879. 

it 

it 

tl 

n 

xxvi.,  1881. 

t( 

it 

a 

<( 

xxxiv.,  1884. 

276    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

I.     Abhandlung  P finger's  ArchiVy  Bd.  xiii.,  1876. 

II. 
III. 
IV. 

V. 

3.  V.  Cyon,  E.     Gesammelte  Physiologische  Arbeitetiy  p.  197  a.  f. 
Berlin,  1888. 

4.  MuNK,  H.     Ueber  die  Functionen  der  Grosshirnrinde.     Ber- 
lin, 1881. 

5.  LoEB,  J.      Die  Sehstorungen  nach  Verletzungen  der  Gross- 
hirnrinde.    P finger's  Archiv,  Bd.  xxxiv.,  1884. 

6.  LoEB,  J.     Beitrdge  zur  Physiologie  des  Gross hirns.     PfiUger's 
ArchiVy  Bd.  xxxix.,  1886. 


CHAPTER   XVIII 

DISTURBANCES  OF  ASSOCIATIVE  MEMORY 

I.  We  have  mentioned  the  hypothesis  that  each 
image  of  memory  is  localised  in  a  special  ganglion-cell 
or  a  group  of  ganglion-cells.  As  soon  as  a  new  image 
of  memory  arrives,  it  is,  according  to  this  hypothesis, 
deposited  in  one  of  the  empty  cells.  Who  deposits  it 
and  who  finds  out  which  cell  is  empty  and  which  oc- 
cupied is  a  question  the  originators  of  such  hypotheses 
do  not  ask.  This  conception  treats  the  image  of 
memory  as  if  it  were  something  substantial,  u  e., 
something  characterised  by  mass.^  Munk  has  as- 
serted the  possibility  of  proving  that  in  a  dog  the  sin- 
gle visual  images  of  memory  are  localised  in  isolated 
cells,  or  groups  of  cells,  at  the  part  A^  (Fig.  39).  He 
gives  as  proof  two  experiments,  **  in  which  extirpation 
of  the  part  Aj  caused  the  loss  of  all  but  one  of  the 
visual  images  of  memory.      One  single  visual  image 

'  This  peculiar  hybrid  between  metaphysics  and  anatomy  owes  its  origin 
largely  to  Gall.  Gall  was  an  industrious  worker  in  the  anatomy  of  the  brain 
and  at  the  same  time  a  huge  fraud.  The  anatomy  of  the  brain  was  not  suffi- 
ciently sensational  for  him,  so  he  enlivened  things  somewhat  by  grafting  upon 
his  anatomy  the  worst  metaphysics  he  could  possibly  get  hold  of.  The  various 
nooks  and  corners  of  the  brain  became  the  seat  of  soul-powers  of  his  invention. 
This  artificial  connection  between  metaphysics  and  brain-anatomy  or  histology 
has  since  become  traditional. 

277 


278    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

of  memory  in  each  case  was  found  to  be  preserved  and 
unimpaired  :  in  one  case  the  image  of  the  pail,  out  of 
which  the  dog  was  accustomed  to  drink,  remained  ;  in 
the  other,  that  of  the  motion  of  the  hand,  which  be- 
fore the  operation  had  been  the  signal  for  the  dog  to 
give  its  paw."  It  was  this  statement  of  Munk  that 
led  me  as  a  student  to  make  experiments  on  the 
brain.  I  hoped  that  a  road  to  an  exact  psychology 
had  been  opened.  I  began  my  experiments  as  a  con- 
firmed supporter  of  Munk.  The  more  experiments 
I  made  the  more  it  became  apparent  that  many  of 
Munk's  statements  were  incorrect,  especially  his  mea- 
gre statements  concerning  the  supposed  localisation 
of  single  images  of  memory.  It  is  my  opinion  that 
these  histological  or  corpuscular  hypotheses  of  the 
images  of  memory  must  be  supplanted  by  dynamical 
conceptions.  The  dynamics  of  the  process  of  associ- 
ation is  the  true  problem  of  brain-physiology.  Even  if 
the  hypotheses  of  psychic  localisation  were  not  contra- 
dicted by  all  the  facts,  the  pointing  out  of  the  centres 
would  not  be  a  solution  of  the  dynamical  problem. 
By  merely  showing  a  student  the  location  of  a  power- 
plant,  we  do  not  explain  to  him  the  dynamics  of 
electric  motors. 

I  have  mentioned  above  the  possibility  that  pro- 
cesses of  association  will  become  abnormal  if  certain 
elemental  constituents  are  mutilated  or  impossible. 
I  selected  as  an  example  our  ability  to  recognise 
a  vowel.  If  the  vowel  is  sung  at  a  pitch  which 
excludes    its    specific    formative   sound,    it   becomes 


DISTURBANCES  OF  MEMORY  279 

indistinct.  A  study  of  patients  afflicted  with  amnesia 
seems  to  support  this  analogy.  It  is  not  possible  to 
use  all  the  reports  of  such  cases.  I  think  that  the 
majority  of  practitioners  have  neither  the  training  nor 
the  time  to  analyse  them.  I  will  confine  myself  to 
two  cases  from  the  Clinic  of  Professor  Rieger  in 
Wurzburg,  one  of  which  was  analysed  by  himself  (i), 
and  the  other  by  his  assistant,  Dr.  Wolff  (2).  In  the 
first  case  the  patient  had  suffered  a  concussion  of  the 
brain  in  a  railroad  accident.  Among  a  number  of 
other  disturbances,  his  memory  showed  peculiar  gaps. 
The  patient  was  able  to  recognise  only  the  numbers 
I,  2,  and  3.  The  corpuscular  theory  of  the  images  of 
memory  would  assume  that  all  numbers  which  the  pa- 
tient had  originally  possessed  had  been  located  each 
in  a  special  cell,  and  that  these  cells  had  all  perished 
with  the  exception  of  the  cells  which  contained  the 
first  three  numbers.  This  at  once  seems  strange  ,and 
becomes  still  stranger  when  taken  in  connection  with 
the  following  observation.  In  every  case  it  took  the 
patient  some  time  to  find  the  word  one  when  the  fig- 
ure I  was  held  before  him.  The  reaction-time  for 
naming  a  2  was  considerably  longer,  and  for  naming  a 
3  was  still  longer.  He  was  able  to  reckon  with  these 
three  numbers,  but  when  a  3  occurred  he  required  more 
time  than  when  a  i  or  a  2  occurred.  The  determin- 
ation of  the  reaction-time  furnishes  the  explanation  of 
the  fact  that  all  numbers  beyond  3  were  wanting.  All 
of  Rieger's  experiments  on  this  patient  showed  that  if 
he  did  not  succeed  in  finding  the  name  of  an  object 


28o    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

within  a  certain  time  (about  eighteen  seconds)  it  was 
impossible  for  him  to  do  so  at  all.  Now  for  finding 
the  word  three  when  he  was  shown  the  figure  3  he 
required  almost  eighteen  seconds,  and  in  fact  he  even 
failed  occasionally  to  find  it.  The  first  three  numbers 
are  the  ones  that  a  child  first  learns,  and  are  also 
those  used  most  frequently  during  life.  We  know 
that  the  words  we  use  least  are  the  ones  most  liable 
to  vanish  from  our  memory  (for  instance,  the  vocabu- 
lary of  a  foreign  language).  It  is  possible  that  in  the 
brain  of  the  patient  the  processes  were  partly  mu- 
tilated or  rendered  more  difficult.  The  numbers 
used  most  frequently  could  cross  the  threshold  ;  those 
used  less  frequently  could  not.  This  conception  is 
further  confirmed  by  the  fact  that  by  touching  the 
edges  the  patient  was  able  to  distinguish  a  ten-  from 
a  fifty-pfennig  piece,  although  the  numbers  ten  and 
fifty  were  otherwise  gone,  and  as  stamped  on  the 
coins  were  only  hieroglyphics  to  him.  The  money- 
conception  of  the  ten-  and  fifty-pfennig  piece  had 
formed  more  associations  and  clung  more  tenaciously 
to  the  memory  of  this  man,  who  had  to  struggle  for 
his  existence,  than  the  abstract  conceptions  ten  and 
fifty,  which  had  existed  in  his  head  only  as  a  scholas- 
tic luxury.  Hence  any  adequate  idea  of  the  nature  of 
the  disease  of  this  man  must  be  a  dynamic  one.  In 
the  injured  brain  of  this  patient  certain  processes 
were  able  to  take  place  as  before,  except  that  they 
were  less  intense  or  incomplete.  Those  innervations 
forming  constituents  of  relatively  many  or  important 


DISTURBANCES  OF  MEMORY  281 

associations  were  still  possible,  or  occurred  in  a  more 
normal  form,  while  other  innervations  became  impos- 
sible or  were  mutilated.  In  this  case  it  would  be  just 
as  erroneous  to  assume  that  the  single  conceptions  or 
letters  are  all  localised  in  single  cells,  and  that  the 
corresponding  cells  in  the  patient  had  perished,  as  it 
would  be  erroneous  to  conclude  in  a  case  of  interfer- 
ence of  sounds  that  the  source  of  vibration  was 
removed.^ 

2.  The  second  case  mentioned  is  still  clearer  (2). 
The  disturbance  of  associative  memory  was  also 
caused  by  an  accident.  When  the  patient  was  asked 
the  colour  of  the  leaves  of  a  tree,  he  was  unable  to 
answer  the  question  unless  he  was  allowed  to  go  to 
the  window  and  look  at  a  tree.  In  this  case  he  an- 
swered correctly.  As  long  as  he  could  not  see  a  tree 
it  was  impossible  for  him  to  tell  the  colour  of  a  leaf. 
Pieces  of  green,  red,  and  blue  paper  were  put  before 
him,  and  he  was  asked  which  the  leaves  looked  like, 
but  he  was  unable  to  tell.  If  asked  whether  the  trees 
were  blue,  he  answered  that  this  was  possible.  Only 
when  looking  at  a  tree  was  he  able  to  remember  that 
the  leaves  were  green.  When  asked  how  many  legs 
a  horse  has,  he  went  to  the  window  and  waited  until  a 
horse  passed  by.  This  enabled  him  to  find  the  word 
four.  Only  in  winter  was  he  able  to  tell  the  colour  of 
snow.     In  summer  he  admitted  the  possibility  that 

'  Conditions  similar  to  those  that  existed  in  this  patient  can  be  artificially 
produced  by  the  dynamometer-experiments  which  will  be  described  in  the  next 
chapter. 


282    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

snow  is  black.  He  was  once  asked  the  colour  of  the 
blood.  He  opened  a  little  pustule  on  his  hand,  and 
as  soon  as  a  drop  of  blood  came  out  he  gave  the 
answer,  red. 

It  is  obvious  from  these  facts  that  the  patient  un- 
derstood every  question  and  was  sufficiently  intelli- 
gent to  secure  those  impressions  which  allowed  him 
to  answer  the  question.  He  could  tell  the  colour  of 
sugar  if  allowed  to  look  at  it,  but  this  did  not  help 
him  to  tell  whether  or  not  sugar  tastes  bitter.  In 
order  to  do  so  he  had  to  put  the  sugar  into  his  mouth. 
When  a  smooth  piece  of  glass  was  shown  to  him 
he  could  not  tell  that  it  was  smooth  until  he  had 
touched  it. 

Two  things  are  evident — first,  the  patient  was  not 
able  to  remember  any  perceptible  quality  of  an  ob- 
ject unless  the  object  was  under  his  immediate  per- 
ception ;  and  second,  he  remembered  the  various 
qualities  only  if  the  specific  senses  for  these  qualities 
were  affected.  In  a  normal  being  the  word  sugar  or 
the  sight  of  sugar  suffices  to  produce  the  association 
of  its  sweet  taste.  In  this  patient  only  contact  with 
the  tongue  suggested  the  word  sweet,  although  he 
was  intelligent  enough  to  know  how  to  arouse  the 
correct  association. 

The  names  of  a  great  many  objects  may  be  sug- 
gested to  a  normal  person  through  any  of  several  of 
the  senses.  For  example,  we  find  the  word  violin  if 
we  see  the  object  as  well  as  if  we  hear  it  played  with- 
out seeing  it.     The  patient  in  this  case  was  a  violin 


DISTURBANCES  OF  MEMORY  283 

player,  but  it  was  necessary  for  him  to  see  the  instru- 
ment before  he  could  name  it.  When  a  key  was  put 
into  his  pocket  and  he  was  allowed  to  touch  it  he 
could  not  say  what  it  was.  He  could,  however,  find 
the  word  if  he  could  see  the  key  in  the  door.  When 
his  hand  was  put  to  his  ear,  he  could  not  tell  what  he 
touched  unless  he  looked  at  the  doctor's  ear.  When 
the  doctor  covered  his  own  ear,  the  patient  was  un- 
able to  find  the  word.  It  is  obvious  that  in  his  case 
the  visual  perception  was,  on  the  whole,  more  effect- 
ive than  any  other  sensation.  A  sense-perception 
was  necessary  to  call  forth  the  association  of  concrete 
objects,  and  of  the  many  possible  sense-perceptions, 
which  in  normal  cases  might  have  brought  about  the 
word,  the  strongest  alone  in  him  sufficed.  The  word 
umbrella  was  only  suggested  when  the  umbrella  was 
opened.  From  this  we  might  imagine  that  a  change 
in  the  machinery  of  association  had  taken  place,  which 
allowed  only  the  processes  having  a  maximal  intens- 
ity or  amplitude  to  arouse  an  associative  process,  the 
others  remaining  without  any  effect. 

The  process  was  the  same  in  regard  to  abstract  as- 
sociations. The  patient  complained  that  his  annuity 
was  too  small.  He  remonstrated  against  the  doctor's 
insinuation  that  he  had  murdered  his  wife  or  that  he 
was  a  scamp.  But  whether  a  beggar  is  a  wealthy 
or  a  poor  man,  or  whether  God  lives  in  hell  or  in 
heaven,  were  problems  which  he  was  not  able  to  de- 
cide, although  he  was  a  believer. 

There  was  another  peculiarity  in  his  mechanism  of 


284    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

association  which  is  in  line  with  the  necessity  for 
sense-impressions  for  the  remembrance  of  words. 
Before  he  was  able  to  pronounce  a  word  he  had  to 
go  through  the  motion  of  writing  it.  When  asked 
the  colour  of  the  leaves,  he  had  to  go  to  the  window 
and  look  at  a  tree,  and  then  he  had  to  go  through 
the  motion  of  writing  the  word  green  with  his  finger 
before  he  could  give  the  correct  answer.  When  not 
allowed  to  use  his  fingers  for  this  purpose,  he  used  his 
toes,  and  when  this  was  forbidden,  he  made  the  writing 
motions  in  his  mouth  with  his  tongue.  When  all 
three  motions  were  forbidden,  he  was  not  able  to  find 
the  word.^  He  did  not  write  phonetically,  but  ortho- 
graphically.  It  would  be  absurd  to  think  for  a  mo- 
ment that  in  this  case  one  single  centre,  or  one  single 
tract  between  two  centres,  was  injured.  The  whole 
apparatus  was  equally  affected.  I  believe  that  the 
associative  mechanism  of  the  patient  differed  only 
in  degree  from  the  associative  mechanism  of  a 
normal  being.  Wolff  pointed  out  that  for  each  act 
of  remembering  there  is  one  association  more  power- 
ful than  the  rest.  But  for  a  normal  being  the  weaker 
associations  are  sufficient  for  the  reproduction,  while 
in  our  patient  only  the  strongest  one  sufificed.  One 
may  ask  how  it  happens  that  we  so  seldom  hear  of 
such  simple,  clear  cases  as  those  published  by  Rieger 
and  Wolff.  I  believe  the  majority  of  physicians  who 
deal  with  such  patients  have  neither   the   scientific 

^  It  was  not  necessary  for  him  to  see  what  he  wrote  or  to  actually  write  ;  it 
was  sufi&cient  to  go  through  the  motions  of  writing. 


» 


DISTURBANCES  OF  MEMORY  285 

training  nor  sufficient  time  to  make  an  exhaustive 
analysis  of  the  case.  Wolff's  patient  had  been  in  the 
hands  of  half  a  dozen  specialists,  and  they  discovered 
only  the  peculiar  writing  motions  that  the  patient  used. 
This  of  course  led  them  to  false  conclusions.  If  the 
analysis  in  such  a  case  is  incomplete,  the  results  must 
be  misleading. 

3.  It  is  worth  while  to  compare  the  mental  con- 
dition of  these  patients  with  that  of  lower  animals. 
The  two  patients  mentioned  above  forgot  immedi- 
ately what  was  said  to  them.  If  the  correct  associa- 
tion did  not  occur  to  them  after  a  short  time,  the 
question  had  to  be  repeated.  There  was,  however, 
one  exception.  Objects  or  occurrences  which  were 
intimately  connected  with  their  instincts  they  remem- 
bered— for  instance,  money  matters.  We  can  imagine 
that  conditions  maybe  similar  in  lower  animals — e.  g., 
wasps,  which  either  forget  easily  or  only  seem  to  re- 
member certain  things  which  are  intimately  connected 
with  their  instincts — e.  g.,  the  location  of  the  nest. 

A  qualitative  difference  has  been  supposed  to  exist 
between  the  associative  memory  of  man  and  that  of 
animals.  These  patients  may  help  us  to  arrive  at  a 
decision  in  regard  to  this  question.  When  the  patient 
was  asked  the  colour  of  blood,  the  question  aroused 
associations  which  caused  him  to  provide  the  visual 
impression  of  blood.  If  we  compare  with  this  the 
fact  that  a  wasp  is  no  longer  able  to  find  its  nest 
when  the  latter  is  covered  with  a  small  blossom,  we 
might  imagine  that  there  is  a  qualitative  difference 


286    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

between  the  associative  memory  of  the  wasp  and  of 
man.  It  might  be  argued  that  man  possessed  the 
power  of  creating  new  associations,  i.  e.^  the  abiHty 
of  substituting  or  changing  the  existing  conditions,  in 
order  to  make  a  new  process  of  association  possible. 
But  this  abiHty  is  not  entirely  lacking  in  animals. 
When  in  Thorndike's  experiment  a  cat  goes  volunta- 
rily into  a  certain  cage  and  waits  there  to  be  offered  a 
fish,  we  have  to  deal  with  the  same  apparent  ability 
of  creating  new  associations.  On  the  other  hand,  the 
superiority  of  man  in  this  direction  can  be  accounted 
for  by  the  fact  that  his  capacity  for  forming  and  re- 
taining new  associations  is  very  much  greater  than 
that  of  animals. 

The  question.  What  is  the  colour  of  blood  ?  pro- 
duces not  only  one  association  —  the  word  red —  but 
a  number  of  other  associations,  for  instance,  the  asso- 
ciation of  a  wound  and  the  association  of  the  produc- 
tion of  a  wound.  If  at  that  time  the  sense-impression 
of  a  pustule  occurs,  the  association  arises  that  the 
opening  of  the  pustule  causes  the  appearance  of 
blood.  All  experiments  point  to  the  fact  that  this 
overwhelming  abundance  of  associations  which  even 
a  disabled  human  brain  can  form  is  lacking  in  animals. 
One  impression  may  arouse  only  a  very  limited  num- 
ber of  associations.  This  is  evident  from  Thorndike's 
experiments  on  dogs  and  cats  (3),  and  from  Whit- 
man's observations  on  pigeons  (4).  This  small  capacity 
for  associations  makes  the  reactions  of  animals  appear 
machine-like  and  less  intelligent.      I  think  that  the 


DISTURBANCES  OF  MEMORY  287 

greater  capacity  of  the  human  brain  for  associations 
and  the  greater  celerity  with  which  these  associations 
are  formed  and  retained  are  sufficient  to  explain  why 
mankind  has  been  able  to  control  nature,  while  animals 
remain  at  its  mercy. 

In  a  pamphlet  on  Instinct  and  Intelligence,  Father 
E.  Wasmann,  S.J.,  a  well-known  entomologist,  has 
raised  the  question  as  to  whether  or  not  animals  pos- 
sess intelligence  (5).  The  answer  to  such  questions 
varies  with  the  definition  of  the  word  intelligence,  and 
hence  such  discussions  result  in  a  discussion  of  words 
and  definitions.  Such  scholastic  discussions  are  very 
serviceable  for  the  defence  of  a  dogma  or  an  opinion. 
Wasmann's  pamphlet  belongs  in  this  category.  But 
we  cannot  overlook  the  fact  that  the  steady  progress 
of  science  dates  from  the  day  when  Galileo  freed  sci- 
ence from  the  yoke  of  this  sterile  scholastic  method. 
The  aim  of  modern  biology  is  no  longer  word-discus- 
sions, but  the  control  of  life-phenomena.  Accordingly 
we  do  not  raise  and  discuss  the  question  as  to  whether 
or  not  animals  possess  intelligence,  but  we  consider  it 
our  aim  to  work  out  the  dynamics  of  the  processes  of 
association,  and  find  out  the  physical  or  chemical  con- 
ditions which  determine  the  variation  in  the  capacity 
of  memory  in  the  various  organisms. 

Bibliography. 

I.  RiEGER,  K.  B esc hrei bung  einer  Intelligenzstorung  in  Folge 
einer  Hirnverletzungy  etc.  Verhandl.  der  Wurzburger  physikalisch 
medicinischen  Gesellschaft,  Bd.  xxii.  and  xxiii.,  1889  and  1890. 


288    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

2.  Wolff,  Gustav.  Ueber  krankhafte  Dissoziation  der  Vor- 
stellungen.  Zeitschrift  filr  Psychologie  und  Physiologie  der  Sinnes- 
organe,  Bd.  xv.,  1897. 

3.  Thorndike,  E.  L.  Animal  Intelligence.  The  Psychological 
Review,  vol.  ii.,  1898. 

4.  Whitman,  C.  O.  Animal  Behaviour.  Biological  Lectures 
Delivered  at  Wood's  Holl,  1898.     Boston,  Ginn  &  Co. 

5.  Wasmann,  E.  Instinct  und  Intelligenz  im  Thierreich, 
Freiburg,  1897. 


CHAPTER  XIX 

ON    SOME    STARTING-POINTS    FOR    A    FUTURE 

ANALYSIS  OF  THE  MECHANICS  OF  ASSO- 

CIA  TIVE  MEM  OR  V 

I.  The  facts  have  thus  far  shown  that  the  reflexes 
are  determined  chiefly  by  the  structure  of  the  sense- 
organs,  or  of  the  surface  of  the  body,  and  the  arrange- 
ment of  the  muscles.  The  central  nervous  system 
participates  in  these  functions  only  as  a  conductor. 
The  true  problem  with  which  the  physiology  of  the 
reflexes  is  concerned  is  the  mechanics  of  protoplasmic 
conductivity.  This  problem  is  no  longer  a  biological 
problem  but  a  problem  of  physical  chemistry. 

The  only  specific  function  of  the  brain,  or  certain 
parts  of  it,  which  we  have  been  able  to  find  is  the 
activity  of  associative  memory.  There  is  at  present  a 
tendency  to  consider  the  anatomical  and  histological 
investigation  of  the  brain  as  the  most  promising  line 
for  the  analysis  of  these  functions.  It  seems  to  me 
that  we  can  no  more  expect  to  unravel  the  mechan- 
ism of  associative  memory  by  histological  or  morpho- 
logical methods  than  we  can  expect  to  unravel  the 
dynamics  of  electrical  phenomena  by  a  microscopic 

study  of  cross-sections  through  a  telegraph  wire  or  by 
19  289 


290    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

counting  and  locating  the  telephone  connections  in  a 
big  city. 

If  we  are  anxious  to  develop  a  dynamics  of  the 
various  life-phenomena,  we  must  remember  that  the 
colloidal  substances  are  the  machines  which  produce 
the  life-phenomena.  But  the  physics  of  these  sub- 
stances is  still  a  science  of  the  future.  The  new 
methods  and  conceptions  created  by  physical  chemis- 
try give  us  the  hope  that  a  physics  of  the  colloidal 
substances  may  be  looked  for  in  the  near  future.  At 
present  we  can  only  consider  data  of  secondary  im- 
portance for  the  mechanics  of  associative  memory. 
The  first  group  of  these  data  is  furnished  by  the 
study  of  the  functions  of  the  sense-organs. 

Helmholtz  emphasised  the  fact  that  our  senses  only 
furnish  us  symbols  of  the  external  world.  Every 
physical  process  that  affects  a  sense-organ  produces 
changes  in  the  organ.  These  changes  are  determined 
by  the  peripheral  structure  or  by  the  specific  "  energy  " 
of  the  sense-organs,  as  physiologists  since  Johannes 
Muller  call  it.  Whether  a  blow,  an  electric  current, 
or  ether-vibrations  of  about  0.0008-0.0004  mm.  wave- 
length stimulate  the  retina,  the  sensation  is  always  a 
specific  one,  namely,  light,  while  a  blow  or  an  electric 
current  produces  sensations  of  sound  in  the  ear. 
This  so-called  law  of  the  specific  energy  of  the  sense- 
organs  is  not  peculiar  to  the  sense-organs  ;  it  applies, 
as  was  emphasised  by  Sachs,  to  all  living  matter ;  it 
even  holds  good  for  machines.  It  is  in  reality  only 
another  expression  for  the  fact  that  the  eye,  the  ear, 


FUTURE  ANALYSIS  OF  MEMORY  291 

and  every  living  organ  are  able  to  convert  energy  in 
but  one  definite  form  —  that  is,  that  they  are  special 
machines.  The  determination  of  the  way  in  which 
this  transformation  of  energy  occurs  in  the  various 
organs  would  be  the  explanation  of  the  specific  energy 
of  the  various  senses. 

Physiology  gives  us  no  answer  to  the  latter  ques- 
tion. The  idea  of  specific  energy  has  always  been 
regarded  as  the  terminus  for  the  investigation  of  the 
sense-organs.  All  the  more  credit  is  due  Mach  and 
Hering  for  first  having  advanced  beyond  that  limit 
with  their  chemical  theory  of  colour-sensations.  Mach 
has  recently  expressed  the  opinion  that  chemical 
conditions  lie  at  the  foundation  of  sensations  in 
general  (i). 

For  the  eye  we  may  consider  it  as  probable  that 
light  produces  chemical  effects.  Various  substances 
are  formed  and  decomposed  in  the  retina,  and  the 
chemical  processes  of  the  formation  and  decomposi- 
tion of  these  substances  determine  the  light-  and 
colour-sensations.  The  ether-vibrations  of  certain 
wave-lengths  influence  these  decompositions  in  a  de- 
finite manner.  The  electro-magnetic  theory  of  light 
will  probably  in  this  case  lead  to  further  discoveries. 
Effects  similar  to  those  produced  by  light  are  also 
brought  about  by  the  electric  current.  The  current 
itself  can  pass  through  the  retina  only  by  means  of 
electrolysis,  and  it  may  be  that  the  increase  in  the 
concentration  of  ions  (wherever  their  progress  is 
blocked)  brings  about  the  light-  and  colour-sensations 


292    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

caused  by  the  current.  It  is  not  impossible  that  the 
so-called  visual  substances — that  is,  the  photo-sensi- 
tive substances — are  electrolytes.  We  can  thus  under- 
stand how  the  electric  current  produces  sensations  of 
light  and  colour  in  the  eye.  But  it  is  more  difficult  to 
account  for  the  fact  that  pressure  or  a  blow  on  the 
eyeball  produces  the  sensation  of  a  flash.  Carey  Lea 
has  found  that  on  photographic  plates  pressure  pro- 
duces changes  of  the  same  character  as  weak  light. 

The  specific  energy  of  the  eye  would  accordingly 
amount  to  nothing  more  than  the  fact  that  an  increase 
in  the  concentration  of  ions  or  certain  other  chemical 
substances  in  the  retina  causes  the  sensation  of  light 
and  colour,  no  matter  whether  the  changes  are  caused 
by  vibrations  of  the  ether,  by  the  electric  current,  or 
by  a  blow  on  the  eye.  The  stimuli  which  are  trans- 
mitted to  the  brain  from  the  eye  will  hence  show  ex- 
actly the  variety  and  peculiarities  which  correspond 
to  the  variety  and  peculiarities  of  the  chemical  pro- 
cesses in  the  retina. 

The  same  holds  good  for  the  stimuli  which  are 
transmitted  to  the  brain  from  the  organs  of  taste  and 
from  the  nose.  The  chemical  nature  of  the  causes 
that  produce  the  sensations  of  smell  and  taste  is  so 
apparent  as  to  require  no  proof. 

We  find  greater  difficulty  in  dealing  with  the  sense- 
organs  of  the  skin.  Yet  it  is  conceivable  that  a  chem- 
ical basis  may  also  exist  for  the  activity  of  these  senses. 
This  idea  finds  support  in  a  train  of  thought,  by  which 
I  attempted  to  explain  the  peculiar  influence  of  grav- 


FUTURE  ANALYSIS  OF  MEMORY  293 

ity  on  the  orientation  of  animals  and  plants  and  their 
formation  of  organs  (2).  In  these  cases,  a  change 
in  the  orientation  of  the  organs  produces  a  change  in 
the  chemical  condition.  If  the  chemical  processes  in 
these  instances  consist  in  fermentative  processes,  the 
amount  of  the  chemical  change  in  the  unit  of  time 
must  be  a  function  of  the  number  of  the  ferment-mole- 
cules and  of  the  fermentable  molecules  that  come  in 
contact.  If  we  assume  that  both  are  present  in  dif- 
ferent morphological  constituents  of  the  living  cells, 
that  the  ferment,  for  instance,  is  present  in  the  nu- 
cleus, the  fermentable  substance  in  the  protoplasm  of 
the  cell,  it  is  apparent  that  a  change  in  the  position 
of  the  cell  or  a  pressure  upon  it  will  bring  new  mole- 
cules of  the  protoplasm  in  contact  with  the  nucleus. 
In  this  way  the  metabolic  activity  may  be  increased. 
Such  changes  in  the  peripheral  nerve-endings  of  the 
skin  might  result  in  innervations  and  reflexes.  But 
this  is  all  so  vague  that  it  only  indicates  the  possibil- 
ity of  the  chemical  character  of  the  process.  It  seems 
forced,  if  not  altogether  impossible,  to  apply  this 
theory  to  the  cochlea  of  the  ear.  We  could  imagine 
that  the  vibrations  of  sound  produce  corresponding 
vibrations  in  the  endings  of  the  auditory  nerve,  by 
which  new  molecules  are  brought  into  contact  with 
each  other.  But  I  cannot  see  how  this  assumption 
could  account  for  the  different  pitches  or  the  phenom- 
ena of  consonance.  While  a  chemical  theory  is  pos- 
sible or  probable  for  certain  sensations,  e.  g.,  light, 
taste,  and  smell,  it  is  very  doubtful  whether  such  a 


294    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

theory  can  be  applied  to  the  other  sense-organs.  But 
it  is  certain  that  if  we  wish  to  make  any  progress  in 
this  direction  we  must  follow  the  lead  of  Mach  and 
Herinof,  and  must  cease  to  consider  the  so-called 
law  of  the  specific  energy  of  the  sense-organs  as  the 
terminus  of  our  investigation  of  the  processes  of 
sensation. 

2.  If  we  wish  to  find  out  the  dynamics  of  associa- 
tion we  must  study  the  effects  which  simultaneous 
processes  have  upon  each  other.  Let  us  consider 
periodic  and  aperiodic  processes. 

If  we  turn  a  wheel  with  one  hand  without  thinking 
of  the  manner  or  velocity  of  the  rotation,  and  at  the 
same  time  repeat  a  poem  to  ourselves  without  moving 
the  lips,  the  number  of  the  revolutions  shows  a  simple 
numerical  relation  to  the  number  of  the  arses  of  the 
verses.  In  German,  where  the  arsis  is  pronounced 
with  greater  emphasis  than  the  thesis,  the  number  of 
the  rotations  of  the  wheel  generally  equals  the  num- 
ber of  the  arses.  Briicke  first  called  attention  to  this 
relation.  Thirteen  years  ago  I  made  a  large  number 
of  experiments  (not  published)  concerning  this  sub- 
ject that  yielded  the  same  result.  But  I  found,  fur- 
ther, that  if  one  intentionally  turns  the  wheel  rapidly 
and  recites  slowly,  the  number  of  rotations  is  a  simple 
multiple  of  the  arses.  Two,  three,  or  even  more  re- 
volutions are  made  in  the  interval  of  one  arsis.  If  one 
recites  very  rapidly  and  turns  the  wheel  very  slowly, 
the  number  of  the  arses  becomes  a  simple  multiple  of 
the  number  of  revolutions.     In  the  latter  case,  the 


FUTURE  ANALYSIS  OF  MEMORY  295 

number  of  revolutions  is  often  the  same  as  the  num- 
ber of  verses.  If  we  assume  that  in  thinking  the 
poem  the  respiratory  innervations  which  follow  the 
rhythm  can  be  represented  as  harmonic  curves,  and 
that  the  same  holds  good  for  the  innervations  which 
are  responsible  for  the  turning  of  the  wheel,  it  follows 
from  these  facts  that  harmonic  processes  of  innervation 
occurring  simulta?ieously  affect  each  other  in  such  a 
way  that  the  periods  of  both  processes  are  either  equal 
or  in  the  ratio  of  simple  m^ultiples  of  each  other.  It 
requires  great  determination  to  withstand  this  law.  I 
consider  it  possible  that  where  this  succeeds  the  de- 
viation from  the  law  is  only  apparent,  not  real.  In 
reality  it  might  be  possible  that  one  of  the  two  har- 
monic processes  was  stopped  temporarily.  The  facts, 
however,  suffice  to  show  that  two  harmonic  processes 
of  innervation  for  different  parts  of  the  body,  occur- 
ring simultg.neously,  influence  each  other  and  are  most 
liable  to  form  processes  of  equal  period. 

The  same  is  true  not  only  for  two  or  more  simulta- 
neous processes  of  motor  innervation,  but  also  for 
simultaneous  sensory  processes  and  motor  innerva- 
tions, as  is  proved  by  dancing.  The  rhythm  of  the 
music  and  the  period  of  the  motor  innervations  of  the 
legs  and  body  coincide. 

3.  A  priori  it  would  follow  from  these  facts  that 
two  simultaneous  aperiodic  processes  will  in  general 
interfere  with  or  inhibit  each  other.  That  this  is  to 
a  certain  extent  true  is  shown  by  the  experience  that 
we  cannot  do  two  thines  well  at  the  same  time.     We 


296    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

must  add,  however,  the  provision  that  the  two  things 
are  aperiodic.  If  they  be  periodic,  the  opposite  is 
true.  We  cannot  solve  an  equation  while  jumping 
over  a  broad  ditch.  According  to  Fechner's  inter- 
pretation of  this  fact  the  brain  at  any  time  has  only  a 
certain  amount  of  energy  at  its  disposal.  In  jump- 
ing over  a  ditch  all  the  energy  is  supposed  to  pass 
into  the  muscles  and  nothing  is  left  for  the  process 
of  thinking.  I  showed  fourteen  years  ago  that  Fech- 
ner's conception  was  not  correct.  The  inhibition  of 
a  process  of  thought  by  simultaneous  muscular  ac- 
tivity is  greater  when  we  innervate  one  arm  than 
when  we  innervate  both  arms  simultaneously.  Ac- 
cording to  Fechner,  however,  the  greater  the  number 
of  muscle-groups  that  were  innervated  the  more 
energy  must  be  consumed  in  the  brain.  In  these  ex- 
periments I  measured  the  maximal  pressure  which 
the  flexors  of  the  hand  afe  able  to  exert  on  a  dynamo- 
meter. This  pressure  does  not  decrease  when  the 
other  hand  or  all  the  muscles  are  innervated  simul- 
taneously, but  even  increases  (3).  The  further  appli- 
cation of  this  method  explained  the  fact  that  we 
cannot  well  be  mentally  and  physically  active  at  the 
same  time. 

If  we  begin  by  solving  a  moderately  difficult  prob- 
lem in  mental  number  work,  and  if  we  attempt  when 
in  the  midst  of  the  task  to  attain  the  highest  dynamo- 
metrical  pressure  with  the  hand,  the  pressure  re- 
mains from  20-30^  below  the  maximum  that  we 
otherwise  attain  when  we  devote  our  attention  to  the 


FUTURE  ANALYSIS  OF  MEMORY  297 

pressure  alone  (3,  4).  It  often  occurs,  however,  that 
the  maximal  pressure  is  obtained  while  reckoning. 
In  this  case  the  experimenter  certainly  interrupted 
his  reckoning  while  pressing.  This  is  shown  by  the 
fact  that  in  this  case  either  the  task  is  not  solved  cor- 
rectly or  the  problem  is  entirely  forgotten  by  the 
subject  experimented  upon.  It  was  a  great  excep- 
tion if  the  maximal  pressure  was  attained  and  the 
task  also  solved  correctly.  The  experiments  result 
quite  differently,  however,  when  the  experimenter 
first  begins  by  pressing,  and  the  problem  is  given 
when  the  maximal  pressure  has  already  been  reached, 
so  that  it  is  only  necessary  to  keep  up  the  pressure. 
In  this  case  I  noticed  no,  or  only  a  very  slight,  in- 
fluence of  both  activities  :  the  person  could  reckon 
correctly,  although  with  effort,  and  the  curve  either 
did  not  descend,  or  descended  but  little  lower  than 
without  the  reckoning. 

Thus  we  see  that  a  simultaneous,  static  innerva- 
tion, no  matter  how  strong,  does  not  prevent  the 
reckoning  ;  that,  on  the  other  hand,  a  rapidly  increas- 
ing maximal  motor  innervation  disturbs  the  process 
of  reckoning  perceptibly.  I  have  attempted  to  dis- 
cover whether  a  sudden  stoppage  of  motor  innerv- 
ation— that  is,  a  sudden  relaxation  of  the  statically 
contracted  muscles — disturbs  the  process  of  reckon- 
ing.    This  is  not  the  case. 

Whatever  may  be  the  explanation  of  these  phe- 
nomena, we  see  that  two  simultaneous,  maximal, 
aperiodic  processes  of  innervation  which  require  an 


298    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

effort  disturb  each  other.  On  the  other  hand,  if  they 
have  not  a  maximal  intensity  they  can  take  place  simul- 
taneously. I  fottnd  that  easy  tasks  07"-  the  reproduc- 
tion of  simple  matters  of  m^emory  did  not  lower  the 
maxiTfium  of  the  pressure. 

4.  These  experiments  recall  the  disturbances  of 
associative  memory  which  were  discussed  in  the 
preceding  chapter.  By  causing  powerful  processes 
of  motor  innervation  to  go  on,  we  interfere  with 
all  associations,  except  those  which  have  occurred 
very  frequently.  This  was  the  characteristic  of  the 
patients  mentioned  in  the  preceding  chapter.  But  at 
the  same  time  it  does  not  exhaust  the  case.  The 
processes  of  innervation  in  the  brain  of  these  patients 
were  possibly  mutilated  not  only  in  intensity  but  also 
in  other  dimensions  or  directions. 

Perhaps  the  cases  of  the  inhibition  of  reflexes  also 
belong  in  this  same  category  of  phenomena.  We 
have  mentioned  that  a  dog  with  severed  spinal  cord 
shows  pendulum-movements  of  the  hind-legs  when 
they  are  allowed  to  hang  down.  But  if  we  press  the 
skin  of  the  tail  gently  the  pendulum-movements  of 
the  legs  at  once  cease  (Goltz).  Some  authors  seem 
to  be  under  the  impression  that  a  shock-effect  must 
consist  in  the  exhaustion  of  the  parts  under  the  in- 
fluence of  the  shock.  This  is  not  necessarily  true. 
The  shock-effect  may  be  due  to  a  phenomenon  of 
interference  or  to  a  comparatively  slight  physical 
change  which  results  in  a  mutilation  of  the  processes 
of  innervation. 


FUTURE  ANALYSIS  OF  MEMORY  299 

The  r6le  which  the  intensity  plays  in  the  case  of 
two  simultaneous  processes  of  innervation  recalls  the 
influence  two  simultaneous  wave-motions  have  upon 
each  other.  A  superposition  of  two  waves  is  only 
possible  as  long  as  the  amplitude  is  not  too  great. 
It  looks  as  if  two  processes  can  occur  simultane- 
ously in  our  brain  only  when  their  intensity  is  weak 
enough  to  allow  a  superposition. 

It  is  perhaps  allowable  to  pursue  this  possible 
analogy  of  the  processes  of  innervation  with  wave- 
motions  a  step  farther  and  apply  it  to  the  process  of 
association.  A  process  remains  associated  with  those 
processes  in  our  brain  which  occur  quite  or  almost 
simultaneously.  Let  us  imagine  that  every  process 
in  our  central  nervous  system  has  a  definite  form  in 
so  far  as  it  can  be  represented  by  a  curve  in  which 
the  time-elements  are  represented  by  the  abscissas 
and  the  intensity  of  the  processes  by  the  ordinates. 
If  two  processes  take  place  simultaneously  and  their 
intensity  is  not  too  strong,  they  superpose  each  other. 
The  traces  which  this  process  leaves  in  our  central 
nervous  system  correspond  to  the  curve  which  is  de- 
termined by  the  superposition  of  both  elementary 
curves.  If  one  of  the  processes  takes  place  later  on, 
the  other  process  also  is  reproduced  by  resonance. 
On  the  other  hand,  a  very  complicated  process  may 
reproduce  simpler  processes,  which  are  contained 
in  the  former  as  constituents  and  have  already  oc- 
curred once  before  in  their  simple  form.  Our  ex- 
perience concerning  sound-sensations  shows  indeed 


300    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

that  simultaneous  simple  harmonic  motions  may  in 
our  sensations  fuse  to  a  compound  sound  of  definite 
character  {Klangfarbe).  Moreover,  a  trained  ear  is 
able  to  decompose  a  compound  Klang  into  its  simple 
harmonic  constituents.  The  mechanism  of  associa- 
tive memory  must  share  these  peculiarities  of  our 
organs  for  the  perception  of  sounds.  I  believe  that 
what  we  commonly  call  intelligence  depends  partly 
upon  the  development  of  this  power  of  resonance  of 
the  mechanism  of  association. 

The  existence  of  phenomena  of  resonance  in  our 
nervous  processes  may  account  for  the  fact  that  stim- 
ulation' of  the  same  organ  yields  entirely  different 
results  if  we  change  the  character  or  rhythm  of  stim- 
ulation. Only  certain  sounds  cause  a  dog  to  howl ; 
only  a  certain  way  of  rubbing  the  skin  of  a  frog 
causes  the  animal  to  croak.  The  so-called  law  of 
the  specific  energy  of  the  sense-organs  has  pushed 
these  important  facts  into  the  background  and  has 
tried  to  convey  the  idea  that  the  character  of  the 
stimulation  was  something  indifferent.  Although 
it  is  true  that  a  blow  on  the  eye  gives  rise  to  a 
sensation  of  light,  nobody  would  for  one  instant  mis- 
take this  light-sensation  for  one  caused  by  ether-vi- 
brations. It  is  of  course  impossible  to  throw  light 
on  this  subject  from  the  anatomy  or  histology  of  the 
brain.  But  our  experiences  in  regard  to  sound-sensa- 
tions promise  the  possibility  of  an  analysis  of  these 
phenomena.  Hermann  and  Mach  come  to  the  con- 
clusion that  the  physical  resonance-theory  of  Helm- 


FUTURE  ANALYSIS  OF  MEMORY  301 

holtz  is  no  longer  tenable,  and  that  it  may  have  to  be 
substituted  by  a  physiological  resonance-theory  (6,  7). 
According  to  Hermann,  we  may  assume  that  the 
nervous  end-organs  themselves  are  especially  sens- 
itive for  stimuli  of  a  definite  period  (7).  A  gen- 
eralisation of  this  assumption  would  lead  to  an 
understanding  of  the  above-mentioned  fact.  The 
motor  organs  of  the  larynx  may  be  considered  as 
resonators,  and  this  would  explain  why  only  cer- 
tain tones  cause  a  dog  to  howl  and  why  only  fric- 
tion of  a  certain  character  —  i.  e.,  periods  —  causes  a 
frog  to  croak.  The  fact  of  the  easy  transmission  of 
sounds  into  innervations  to  the  larynx  in  human 
beings  and  parrots  or  song-birds  would  depend  on 
the  same  principle.  But  in  theories  of  this  character 
we  must  leave  some  leeway  for  the  influence  of  chem- 
ical processes.  The  phenomena  of  correlation  which 
we  notice  in  many  animals  during  the  period  of  heat 
may  be  determined  by  substances  circulating  in  the 
blood  during  that  period  (internal  secretion).  This 
may  account  for  the  change  in  the  irritability  during 
that  period. 

5.  Our  space-sensations  are  varieties  of  three  dimen- 
sions. The  main  coordinates  show  a  definite  relation 
to  the  main  axes  of  our  body.  This  leads  us  to  a 
consideration  of  the  possibility  whether  certain  struct- 
ural conditions  of  our  body  determine  the  main  coor- 
dinates of  our  system  of  space-sensations.  Hering 
has  shown  that  the  motor  innervations  of  our  eyes 
may  be  reduced  to  three  kinds,  corresponding  to  the 


302    COMPARATIVE  PHYSIOLOGY  OF  THE  BRAIN 

main  axes  of  our  body  :  (i)  innervations  to  move  our 
eyes  from  right  to  left,  or  vice  versa  ;  (2)  innervations 
to  move  them  up  and  down  ;  and  (3)  move  them 
from  a  near  to  a  far  object,  or  vice  versa  (8).  The 
first  motion  takes  place  along  the  transverse  axis,  the 
second  along  the  longitudinal,  and  the  third  along 
the  dorso-ventral  axis.  The  experiments  on  the  hori- 
zontal semicircular  canals  of  the  ear  show  that  the 
stimulation  of  this  canal  produces  motions  of  the  eyes, 
head,  or  even  of  the  whole  animal  in  the  plane  of  this 
canal.  Our  experiments  on  galvanotropism  indicate 
the  existence  of  a  simple  relation  between  the  orien- 
tation of  certain  motor  elements  in  the  central  nerv- 
ous system  and  the  direction  of  the  motions  produced 
by  their  activity.  This  is  supported  to  a  certain 
extent  by  the  experiments  on  the  crura  cerebelli.  It 
thus  seems  possible  that  simple  geometrical  relations 
of  structure  are  responsible  for  the  fact  that  all  our 
innervations  may  be  reduced  to  three  classes  deter- 
mined by  the  main  axes  of  our  body.  On  the  other 
hand,  Mach  furnished  the  proof  that  the  will  or  the 
process  of  innervation  for  a  motion  is  of  the  same 
character  as  the  process  of  space-sensations  (5,  6). 
The  will  to  move  our  eyes  to  a  certain  point  and 
the  space-sensation  itself  can  be  added  algebraically. 
The  experiences  derived  from  space  illusions  caused 
by  imperfect  motility  of  the  eyes  or  hands  agree  with 
this  view.  Moreover,  Mach  has  proved  that  we  recog- 
nise the  geometrical  symmetry  of  two  figures  very 
easily  only  when  the  axis  of  symmetry  coincides  with 


FUTURE  ANALYSIS  OF  MEMORY  303 

that  of  our  body  (5,  6).  All  these  facts  indicate  that 
the  main  coordinates  of  the  physiological  space  are 
determined  by  structural  peculiarities  of  our  body. 
The  ultimate  structural  elements  in  this  case  are  not 
necessarily  of  a  morphological  or  histological  order. 
They  may  be,  as  Mach  has  intimated  in  another  con- 
nection, the  stereochemical  configuration  of  certain 
molecules  (i).  As  it  is  not  my  intention  to  enter 
here  upon  a  discussion  of  the  nature  of  the  space- 
sensations,  but  to  indicate  what  place  they  may  oc- 
cupy in  a  future  mechanics  of  the  activity  of  the  brain, 
these  hints  may  suffice. 

Bibliography. 

1.  Mach,  E.  DiePrinciptender  Wdrmelehre^^.  ^60.  Leipzig, 
1896. 

2.  LoEB,  J.  Zur  Theorie  der  physiologischen  Licht- und  Schwer- 
kraft-Wirkungen.     Pfluger's  Archiv^  Bd.  Ixvi.,  1897. 

3.  LoEB,  J.  Muskelthdtigkeit  als  Maass  psychischer  Thdtigkeit. 
Pflugers  Archiv^  Bd.  xxxix.,  1886. 

4.  Welch,  J.  C.  On  the  Measurement  of  Mental  Activity  through 
Muscular  Activity^  etc.  The  American  Journal  of  Physiology^ 
vol.  i.,  1898. 

5.  Mach,  E.  Contributions  to  the  Analysis  of  the  Sensations. 
Chicago,  1897. 

6.  Mach,  E.  Die  Analyse  der  Empfindungen  und  das  Verhdlt- 
niss  des  Physischen  zum  Psychischen.     Jena,  1900. 

7.  Hermann,  L.  Beitrdge  zur  Lehre  von  der  Klangwahr- 
nehmung.     Pfliiger's  Archiv^  Bd.  Ivi.,  1894. 

8.  Hering,  E.   Die  Lehre  vom  binocularen  Sehen,    Leipzig,  1 868. 


INDEX 


Acalephae,  16-34,  97 
Acoustic  nerve.     See  Auditory  Nerve. 
Actinians,  41,  48-60,  221,  227,  228 
Amblystoma,  i6<>-i62,  204,  205,  231, 

264 
Amnesia,  277-287 
Amphipyra,  184 
Annelids,  82-100 
Anterior  roots,  113,  135 
Ants,  195,  220-224 
Apathy,  137 
Aphasia.     See  Amnesia. 
Arbacia,  203 
Arnold,  39 
Arthropods,  101-127 
Ascidians,  35-47 

—  heart  of,  28-30 
Association,  9 

—  corpuscular  theory  of,  277 

—  distribution  of,  213,  etc. 

—  disturbances  of,  277,  etc. 

—  dynamical    theory    of,    278,    etc., 

294 

—  relation  to  cerebral   hemispheres, 

236,  etc.,  262,  etc. 

—  relation    to   consciousness,  12-14, 

214,  etc.,  236,  etc. 

—  relation  to  instincts,  196 
Associative    memory.      See    Associa- 
tion. 

Astacus,     See  Crayfish. 

Asterina,  69,  70 

Auditory  nerve,    134,   152,  155,  158, 

172 
Aurelia  aurita,  17 
Automatic   processes,    9,    10,    16-30, 

106,  etc. 

Balanus  perforatus,  192 
Baumann,  207 


Bawden,  258 

Bed-sores,  209 

Bee,  122,  123,  224,  227,  230 

Bell,  136 

Bethe,  45-49,  "4-127,  131,  I55,  I59. 

219-224,  226,  235 
Bickel,  149 
Blasius,  164 

Blood-vessels,  43,  44,  274 
Brown-Sequard,  39 
Briicke,  294 
Budge,  39 

Burrowing  of  worms,  91,  96 
Buttel-Reepen,  v.,  227,  235 
Butterflies,  182,  222 

—  larvae  of,  188 

Carcinus  maenas,  45,  119 

Centres,  in  spinal  cord,  134-149,  273 

—  in  cerebral  hemispheres,  259-276. 

See  also  Localisation. 

Cephalopods,  129 

Cerebellum,  1 71-176 

Cerebral  hemispheres,  extirpation  of, 
in  frog,  236 ;  in  sharks,  236 ;  in 
birds,  238-244  ;  in  dogs,  246- 
248,  262-276 

segmental  theory  of,  260,  etc. 

relation  of,  to  reflexes,  259 

Cerianthus,  52,  56-59 

Changes  in  character  after  injury  of 
the  brain  in  worms,  92-97  ;  in 
Crustaceans,  116  ;  in  Mollusks, 
130 ;  in  frogs,  139  ;  in  dogs,  173 

Character.  See  Changes  of  Char- 
acter. 

Chemical  irritability  in  Actinians,  50  ; 
in  earthworms,  88,  90  ;  in  crusta- 
ceans, iiS.  See  also  Chemo- 
tropism. 


305 


3o6 


INDEX 


Chemical  theory  of  electrotonus,  i6i  ; 
of  instincts,  177-199  :  of  heredity, 
201  -212 ;  of  mental  diseases,  207 ; 
of  sensations,  291-294 

Chemotropism,  88-90,  186-188 

Christiani,  243 

Chun,  193 

Ciona,  35-38 

Circles  of  touch,  211 

Circus-movements.  See  Forced  Move- 
ments. 

Claus,  49 

Colour-sensations,  291 

Compensatory  motions,  143 

Consciousness.     See  Associations. 

Contact  irritability,  54.  See  also 
Stereotropism. 

Coordination,  10 

—  in  dog,  86,  87,  174 

—  in  earthworm,  84-86 

—  in  frog,  139-143 

—  in  Medusa,  23-27,  29-33 

—  of  heart-beat,  25-30 

—  of  respiratory  motions,  107 

—  relation  to  cerebellum,  173 

—  relation  to  memory,  2 16 
Cranial  nerves,  135 
Crayfish,  114,  162 

Crura  cerebelli,  168,  171 

Cucumaria,  66 

Cyon,  v.,  135,  274,  276 

Darwinian  views,  232,  253 
Depth-distribution  of  marine  animals, 
69,  190 

—  migration  of  marine  animals,  190- 

,  593 
Deviation  conjuguie,   151 
Discrimination-power  of  Actinians,  50 
Dog,  reflexes  of,  86,  137 

—  localisation     in     cerebral     hemis- 

pheres, 260-274 

—  removal  of  spinal  cord  of,  43 

— without  cerebral  hemispheres,  246- 

248 
Dohrn,  134 
Donaldson,  258 
Double-headed  Actinians,  52 

—  Planarians,  81,  82 
Duval,  258 

Duyne,  van,  81,  82,  100 
Dynamometer,      experiments     with, 
294-298 


Ear.     See  Auditory  Nerve. 

Earthworm,  84-90 

Echinoderms,  61 

Education,  233 

Eel,  142,  164,  248 

Eimer,  219 

Electrical  stimulation,  160-170,   173, 

264,  290,  291 
Electrotonus,  162,  etc. 
Eledone,  131 
Engelmann,  137 
Eudendrium,  179 
Exner,  250,  258 
Ewald.     See  Goltz  and  Ewald. 

Faivre,  104,  113,  125 

Falcon,  245 

Fechner,  296 

Ferrier,  36,  173,  176 

Fish,  141,  152-154,  175 

Flechsig,  275 

Flourens,    104,    no,    116,    139,    149, 

168,  170-176,  239,  264 
Fly,  larvae  of,  186-188 
Food,  taking  up  of,  after  lesions  of 

hemispheres,  245 
Forced  movements,   105,    119,    150- 

159,  171 
Forel,  233 
Free  will,  234 
Friedlander,  85,  86,  88,  lOO 
Fritsch,  265 
Frog,  spinal  cord,  139-145 

—  cerebral  hemispheres,  139 

—  clasping  reflex,  238 

—  croaking  reflex,  142,  238 
Frontal  lobes  and  intelligence,  275 
Fundulus,  252 

Gall,  277 
Galvanotropism,  178 

—  of  Amblystoma,  160-162 

—  of  crayfish,  163 

—  of  Palsemonetes,  164 

—  theory  of,  161 
Gammarus,  231 

Ganglion,  importance  of,  for  reflexes, 
4,  36,  46 ;  for  coordination,  5, 
20-25,  106 

Ganglion,  trophical  functions,  136 

Garrey,  160,  231 

Gaule,  210,  212 

Geotropism,  120 

—  and  depth-migration,  193 


INDEX 


307 


Geotropism  in  Actinians,  57 

—  in  Cucumaria,  66 

—  in  Echinoderms,  61-71 

—  in  insects,  66 
Geppert,  108 
Golgi,  136,  137 

Goltz,  43,  86,  137,  142,  145.148,  149. 
193,  2CX),  205,  208,  209,  237-239, 
246,  257,  262-268,  275 

—  and  Ewald,  41-44,  47,    145,   149, 

195,  209,  212,  239 
Gonionemus,  17,  etc.,  95 
Graber,  99,  229 

Grafting  in  Medusa.     See  Hargitt. 
Grasshopper,  121 
Groom,  191,  199 

Hargitt,  26,  27 
Heliotropism,  183,  195 

—  in  Asterina,  69 

—  in  Eudendrium,  179 

—  in  caterpillars,  188 

—  in  marine  animals,  190-193 

—  in  moths,  181 

—  transformation  of,  189,  192 
Helmholtz,  242,  290 
Hemiamblyopia,  271-273 
Hemianopia,  151,  270-273 
Heredity,  201-212 

Hering,  158,  242,  290,  301,  303 
Hermann,  231,  300,  303 
Hertwig,  34 

Heteromorphosis,  51,  203 
Hitzig,  265-267,  275 
Hunter,  42 

Hyde,  Ida,  102,  104,  126,  155 
Hydromedusse,  16,  97 
Hydrophilus,  119,  123 

Image  of  memory,  270-272,  277 
Inhibition,    of  progressive    motions, 
117,  155,  171 

—  of  reflexes,  131,  237,  289-303 
Innervation,  its  relation  to  space-sen- 
sation,   168,    300-303  ;   to   wave 
motion,  289-303 

Instincts,  general  remarks,  6-8 

—  relation  to  nervous  system,  194 

—  theory  of,  177-199 
Intelligence,  in  starfish,  65 

—  difference    in    man    and  animals, 

254 


Intelligence,  differences  in  individu- 
als, 254 

—  disturbances  after  injury  to  brain, 

262,  263,  277-287 

—  heredity  of,  211 

—  localisation  of.     See  Associations. 
Ions  and   rhythmical  contraction,  9, 

18-20 
Iris,  39,  40 

Jaeger,  203 

James,  W.,  216,  235 

Janet,  230 

Jelly-fish.     See  Medusae. 

Lang,  99 

Langendorff,  no,  126 

Lea,  292 

Le  Gallois,  no 

Light,  effect  of,  on  Planarians,  79-81 ; 

on     earthworm,    89.      See    also 

Heliotropism. 
Limulus,  102-113 
Lingle,  28 
Localisation,  psychic  and  anatomical, 

259-276 

—  in  cerebral  hemispheres,  134,  259, 

etc. 

—  in  spinal  cord,  134-149 

—  of  images    of    memory,    270-272^ 

277 
Localising  reflex,  30-33 
Locomotion,  centre  of,  140,  157 
Locy,  134 
Longet,  243 
Lubbock,  223 
Luciani,  174,  176 
Lumbricus.     See  Earthworm. 
Lyon,  176 

Mach,  214,  215,  235,  291,  300-303 
Magendie,  171,  175,  176,  240,  264 
Mass  of  brain,  relation  to  intelligence, 

254 
Mathews,  208,  212 
Maxwell,  87,  88,  92,  93,  96,  97,  100, 

164,  167 
Mayer,  197 
McCaskill,  96 

Mechanics  of  brain  activity,  289,  etc. 
Medulla  oblongata,    no,    139,    140- 

143,  152-154,  171-176 
Medusae,  16,  26,  95,  97 


3o8 


INDEX 


Memory.     See  Associations. 
Mental  diseases,  chemical  theory  of, 

207 
Meyer,  148,  149,  212 
Mollusks,  128,  etc. 
Moth,  177-183 
Motor  nerves  in  arthropods,  113 

—  regions  of    cerebral    hemispheres, 

259-273.  277 

MtiUer,  Johannes,  290 

Munk,  269-272,  276 

MUnsterberg,  216,  235 

Muscular  activity,  a  measure  of  men- 
tal activity,  294,  etc. 

Nagel,  60,  228 

Nereis,  83,  87,  90-98,  116 

Neuron,  45,  161 

Nceud  vital.     See  Respiratory  Centre. 

Norman,  65,  229-232,  235 

Occipital  lobes,  262,  269 

Optic  nerve,  150 

Orientation  and  functions  of  elements, 
160-170 

Oxygen,  importance  of,  for  associa- 
tions, 215,  255,  256 

Pain-sensations  in  animal,  229-231 
Palaemonetes,  164,  178 
Parker,  52,  60 

Pars  commissuralis,  139,  140 
Patten,  105 
Peckham,  224,  235 
Pedal  ganglia  of  Mollusks,  131 
Pfluger,  248-251,  258 
Phrenic  nerve,  109 
Phrenology,  277 

Pigeons,  without  cerebral  hemi- 
spheres, 239-244 

—  instincts  of,  196 
Planarians,  72,  etc.,  230 
Plateau,  222 
Pollock,  60 
Polygordius,  193 

Porter,  25,  26,  34,  112,  126 

Porthesia,  188 

Posterior  roots,  113,  135 

Preyer,  64,  70,  71,  219 

Progressive  motion.    See  Spontaneity. 

Psychic  phenomena.    See  Association. 

—  blindness,  269-272 

—  localisation,  259-276 


Pterotrachea,  128 
Purposefulness,  2,  etc.,  177,  etc. 

Quincke,  22,  34 

Reflexes,  general  remarks,  1-6 

—  coordinate  character  of.    See  Coor- 

dination. 

—  special.    See  various  groups  of  ani- 

mals. 

—  without  ganglion,  35-46 
Respiration,   in   relation   to  ganglia, 

107 

—  in  frog,  143 

—  in  higher  animals,  109 
Respiratory  centre,  110-112,  143,  146 
Responsibility,  234 

Rhythmic,  innervations,  294,  etc, 
motion   in   general,   9 ;    in    Me- 
dusae, 18,  etc.  ;  in  heart,  23-30 ; 
in  respiration.     See  Respiration. 

—  theory  of  rhythm,  21 
Ribbert,  195,  206,  212 
Rieger,  279,  287 

Righting  motion  of  Actinians,  56-59  ; 
starfish,  61-65  ;  Planarians,  74  ; 
arthropods,  124 

Rolando,  239 

Rolling  motions.  See  Forced  Move- 
ments. 

Romanes,  18,  24,  31,  34,  63,  71,  219 

Rosenthal,  21 

Sachs,  66,  203,  290 

Salamander,  142,  160,  204 

Schaper,  42,  47,  206,  212 

Schrader,  139,  143,  149,  157,  236-241, 
258 

Schweizer,  164 

Segmental  theory  of  reflexes,  general 
remarks,  82,  147,  148  ;  of  worms, 
82,  etc.  ;  of  Arthropods,  117; 
of  vertebrates,  133,  145  ;  rela- 
tion to  cerebral  hemispheres,  259- 
276 

Self-preservation,  instinct  of,  183 

Semicircular  canals,  167,  168,  176 

Semi-decussation,  150-159 

Sensations,  290,  etc. 

Sexual  cells,  bearers  of  hereditary 
properties,  201 

—  —  influence   of   nervous    system 

upon,  204-211 


INDEX 


309 


Shark,  40,  232 

Sherrington,  158 

Shock-effect,  126,  147,  298 

Sleep,  243,  257 

Space-sensations,  168,  242,  301 

Specific  energy  of  nerves,  290,  etc. 

Speck,  215,  255,  258 

Spencer,  211 

Sphincter  ani,  41 

Spinal  cord,  reflexes  of,  137 

soul,  250 

Spinal  nerves,  134 
Spontaneity,  8 

—  relation  to  central  nervous  system 

in  general,  78 

—  relation  to   cerebral   hemispheres, 

139,  157,  239-242 

—  relation  to  ganglia  in  Arthropods, 

108 

—  relation  to  ganglia  in  Medusae,  18, 

21 

—  relation  to  ganglia  in  Planarians, 

74,  etc.,  77 

—  relation  to  ions.     See  Medusae. 

—  relation  to  supraoesophageal  gan- 

glion, 106,  116,  121,  123,  128 
Squilla,  119,  121 
Starfish,  61,  etc. 
Steinach,  40,  47 
Steiner,  127,  128,  133,  140,  149,  156- 

159,  175,  182 
Stereotropism,  in  Actinians,  59 

—  in  Amphipyra,  184 

—  in  Crustaceans,  119 

—  in  earthworm,  88 

—  in  eel,  248-250 

—  in  Nereis,  92,  93,  185 

—  in  starfish,  65 

—  in  ThysanozoOn,  74 

—  in  Tubularia,  184 
Stinging  reflex  of  bees,  123 
Suboesophageal  ganglion  in  annelids, 

82 

—  in  Astacus,  116,  120 

—  in  bees,  123 

—  in  Limulus,  106 

—  in  Mollusks,  128 
Supraoesophageal  ganglion  in  Arthro- 
pods, 104,  etc.,  114 

—  in  bees,  123 

—  in  Mollusks,  128 

—  in  worms,  90,  92 


Temporal  lobes,  262 
Thalami  optici,  139 
Thorndike,  286,  288 
Threshold  of  stimulation,  46 

—  after  loss  of  ganglion,  37-39 
Thyroid  gland,  207 
ThysanozoQn,  72,  etc. 
Tiaropsis,  31 

Tone  of  muscles,  152-159 

—  after    injury    to     cerebral     hemi- 

spheres, 266-269. 

after  loss   of  supraoesophageal 

ganglion,  117,  124 

—  after  severing   of  posterior  roots, 

135 

—  relation   to  galvanotropism,    160- 

169 
Tornier,  203 
Trigeminus,  136,  209 
Trophic  nerves,  208-210 
Tropisms,    identity    of    animal    and 

plant  heliotropism,  5,  179 

—  importance  of,  for  instincts,  6,  etc., 

178-200 

—  importance  of,  for  psychology,  13, 

221.  etc.,  249 

—  mechanics  of,  161,  179-181,  186- 

190 
Tubularia,  184 
Turtle,  30 

UexkUll,  v.,  130,  133,  156 

Vasomotors.     See  Blood-vessels. 
Veblen,  197 
Visual  spheres,  269-273 
Vulpian,  113,  126,  175 

Ward,  116 

Wasmann,  226,  235,  287,  288 

Wasps,  196,  224-227 

Water-beetle,  123 

Wave  character  of  innervations,  29I 

303 
Welch,  303 

Whitman,  99,  100,  286,  288 
Will,  215,  302 
Wolff,  279,  288 
Worms,  72,  etc.,  229 

Yersin,  122 

Zuntz,  108 


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the  general  trend  of  thinkers  as  to  evolution  and  Darwinism,  finding  limits  to 
both  and  marking  their  usefulness  when  properly  employed." — Hartford 
Post. 

' '  Dr.  Conn  evidently  favors  the  theory,  but  he  does  not  write  as  a  parti- 
san or  to  carry  a  point,  but  simply  to  show  what  has  been  the  result  of  the 
fruitful  labors  of  the  last  twenty-five  years.  As  a  devout  theist,  he  con- 
siders evolution  simply  a  method  of  creation,  and  does  not  believe  that  this 
derogates  from  the  glory  of  the  Divine  Architect." — N.  Y.  Observer. 

G.  P.  PUTNAM'S  SONS, 
New  York :  London : 

27  AND  29  West  230  St.  27  King  William  St.,  Strand. 

[over. 


THE  SCIENCE  SERIES 


Edited  by  J.  McKeen  Cattell,  M.A.,  Ph.D.,  and  F.  E. 
Beddard,  M.A.,  F.R.S. 


I.— The  Study  of  Man.  By  Professor  A.  C.  Haddon,  M.A.,  D.Sc, 
M.R.I.A.  Fully  illustrated.  8°,  $2.00. 
"  A  timely  and  useful  volume.  .  .  .  The  author  wields  a  pleasing  pen  and  knows 
how  to  make  the  subject  attractive.  .  ,  .  The  work  is  calculated  to  spread  among  its 
readers  an  attraction  to  the  science  of  anthropology.  The  author's  observations  are 
exceedingly  genuine  and  his  descriptions  are  vivid." — London  Athenceum. 

2. — The  Groundwork  of  Science.  A  Study  of  Epistemology.  By 
St.  George  Mivart,  F.R.S.    $1.75. 

"  The  book  is  cleverly  written  and  is  one  of  the  best  works  of  its  kind  ever  put  before 
the  public.  It  will  be  interesting  to  all  readers,  and  especially  to  those  interested  in  the 
study  of  science." — New  Haven  Leader, 

3. — Rivers  of  North  America.  A  Reading  Lesson  for  Students  of  Geo- 
graphy and  Geology.  By  Israel  C.  Russell,  Professor  of  Geology, 
University  of  Michigan,  author  of  "  Lakes  of  North  America,"  "  Gla- 
ciers of  North  America,"  "  Volcanoes  of  North  America,"  etc.  Fully 
illustrated.     8°,  $2.00. 

"There  has  not  been  in  the  last  few  years  until  the  present  book  any  authoritative, 
broad  resume  on  the  subject,  modified  and  deepened  as  it  has  been  by  modern  research 
and  reflection,  which  is  couched  in  language  suitable  for  the  multitude.  .  .  .  The  text 
is  as  entertaining  as  it  is  instructive." — Boston  Transcript. 

4. — Earth  Sculpture ;  or,  The  Origin  of  Land-Forms.  By  James 
Geikie,  LL.D.,  D.C.L.,  F.R.S.,  etc.,  Murchison  Professor  of  Geology 
and  Mineralogy  in  the  University  of  Edinburgh ;  author  of  '*  The 
Great  Ice  Age,"  etc.     Fully  illustrated.     8°,  $2.00. 

"  This  volume  is  the  best  popular  and  yet  scientific  treatment  we  know  of  of  the  ori- 
gin and  development  of  land-forms,  and  we  immediately  adopted  it  as  the  best  available 
text-book  for  a  college  course  in  physiography.  .  .  .  The  book  is  full  of  life  and  vigor, 
and  shows  the  sympathetic  touch  of  a  man  deeply  in  love  with  nature." — Science. 

5. — Volcanoes.  By  T.  G.  Bonney,  F.R.S.,  University  College,  London. 
Fully  illustrated.     8°,  $2.00. 

"  It  is  not  only  a  fine  piece  of  work  from  a  scientific  point  of  view,  but  it  is  uncom- 
monly attractive  to  the  general  reader,  and  is  likely  to  have  a  larger  sale  than  most  books 
of  its  cl^ss.^'' —Springfield  Republican. 

6. — Bacteria  :  Especially  as  they  are  related  to  the  economy  of  nature,  to 
industrial  processes,  and  to  the  public  health.  By  George  Newman, 
M.D.,  F.R.S.  (Edin.),  D.P.H.  (Camb.),  etc..  Demonstrator  of  Bac- 
teriology in  King's  College,  London.  With  24  micro-photographs  of 
actual  organisms  and  over  70  other  illustrations.     8°,  $2.00. 

"  Dr.  Newman's  discussions  of  bacteria  and  disease,  of  immunity,  of  antitoxins,  and 
of  methods  of  disinfection,  are  illuminating,  and  are  to  be  commended  to  all  seeking  in- 
formation on  these  points.  Any  discussion  of  bacteria  will  seem  technical  to  the  uniniti- 
ated, but  all  such  will  find  in  this  book  popular  treatment  and  scientific  accuracy  happily 
combined."—  The  Dial. 


7.— A  Book  of  Whales.  By  F.  E.  Beddard,  M.A.,  F.R.S.  Illustrated. 
8°,  $2.00. 

"  Mr.  Beddard  has  done  well  to  devote  a  whole  volume  to  whales.  They  are  worthy 
of  the  biographer  who  has  now  well  grouped  and  described  these  creatures.  The  general 
reader  will  not  find  the  volume  too  technical,  nor  has  the  author  failed  in  his  attempt  to 
produce  a  book  that  shall  be  acceptable  to  the  zodlogist  and  the  naturalist."— A''.  K.  Times. 

8. — Comparative  Physiology  of  the  Brain  and  Comparative  Psy- 
chology. With  special  reference  to  the  Invertebrates.  By  Jacques 
LoEB,  M.D.,  Professor  of  Physiology  in  the  University  of  Chicago. 
Illustrated.     8°,  $1.75. 

*'  No  student  of  this  most  interesting  phase  of  the  problems  of  life  can  afford  to  remain 
in  ignorance  of  the  wide  range  of  facts  and  the  suggestive  series  of  interpretations  which 
Professor  Loeb  has  brought  together  in  this  volume." — Joseph  Jastrow,  in  the  Ckicagv 
Dial. 

9.— The  Stars.  By  Professor  Simon  Newcomb,  U.S.N.,  Nautical  Al- 
manac Office,  and  Johns  Hopkins  University.  8°.  Illustrated.  Net, 
$2.00.     (By  mail,  $2.20.) 

10. — The  Basis  of  Social  Relations.  A  Study  in  Ethnic  Psychology.  By 
Daniel  G.  Brinton,  A.M.,  M.D.,  LL.D.,  Sc.D.,  Late  Professor  of 
American  Archaeology  and  Linguistics  in  the  University  of  Pennsyl- 
vania;  Author  of  "History  of  Primitive  Religions,"  "Races  and 
Peoples,"  "  The  American  Race,"  etc.  Edited  by  Livingston  Far- 
rand,  Columbia  University.     8°.     (By  mail,  $        .)     Net,  $ 


The  following  volumes  are  in  preparation  : 

Meteors  and  Comets.     By  Professor  C.  A.  Young,  Princeton  University. 
The  Measurement  of  the  Earth.     By  Professor  C.  T.  Mendenhall, 

Worcester  Polytechnic  Institute,  formerly  Superintendent  of  the  U.  S. 

Coast  and  Geodetic  Survey. 
Earthquakes.     By  Major  C.  E.  Button,  U.S.A. 
The  History  of  Science.     By  C.  S.  Peirce. 
Recent   Theories   of  Evolution.     By  J.  Mark  Baldwin,  Princeton 

University. 
The  Reproduction  of  Living  Beings.     By  Professor  Marcus  Hartog, 

Queen's  College,  Cork. 
Man  and  the  Higher  Apes.     By  Dr.  A.  Keith,  F.R.C.S. 
Heredity.     By  J.  Arthur  Thompson,  School  of  Medicine,  Edinburgh. 
Life  Areas  of  North  America:    A  Study  in  the   Distribution  of 

Animals  and  Plants.      By  Dr.  C.  Hart  Merriam,  Chief  of  the 

Biological  Survey,  U.  S.  Department  of  Agriculture. 
Age,  Growth,  Sex,  and   Death.     By  Professor  Charles  S.  Minot, 

Harvard  Medical  School. 
History  of  Botany.     By  Professor  A.  H.  Green. 
Planetary  Motion.     By  G.  W.  Hill. 
Infection  and  Immunity.     By  George  M.  Sternberg,  Surgeon-General, 

U.S.A. 


The 
Mental  Functions  of  the  Brain 

An  Investigation  into  their  Localisation  and  their 
Manifestation  in  Health  and  Disease. 

By    Bernard    Hollander,    M.D.    (Freiburg 
i.B.),  M.R.C.S.,  L.R.C.P.  (London.) 

Illustrated  with  the  clinical  records  of  eight  hundred 
cases  of  localised  brain  derangements  and 

with  several  plates.     8°. 
(By  mail,  $3.75.)  Net,  $3.50. 

•*  A  book  which  should  be  read  by  every  Surgeon  and  Physician  in 
America." — Boston  Times. 

"  This  is  a  work  of  more  than  ordinary  importance.  The  author's 
researches  and  results  oblige  him  not  only  to  combat  popular  opin- 
ions, but  to  criticise  rather  sharply  some  high  medical  authorities. 
The  brain  is,  indeed,  the  organ  of  the  mind,  but  the  various  functions 
of  the  mind  have  their  separate  centres  of  activity  in  the  brain.  In 
the  localisation  of  these  centres  good  progress  has  been  made  and  is 
still  to  be  made.  The  great  pioneer  in  this  line  of  discovery  was  Dr. 
Franz  Joseph  Gall,  a  century  ago.  His  results  were  long  discredited 
but  are  here  presented  for  the  first  time  as  largely  confirmed  by  other 
lines  of  research.  The  phenomena  of  various  kinds  of  mania  are  ex- 
hibited by  Dr.  Hollander  in  their  connection  with  local  brain-lesions, 
and  special  memories  for  words,  numbers,  music,  etc.,  are  traced  to 
their  local  centres  in  the  brain.  These  and  cognate  discussions  lead 
on  to  a  strenuous  rehabilitation  of  phrenology,  long  discredited 
through  quackery,  and,  as  Dr.  Hollander  contends,  through  medical 
Philistinism.  The  ability  with  which  Dr.  Hollander  pleads  the  case 
is  commensurate  with  his  courage  in  stemming  the  current  of  adverse 
prejudice.  While  this  work  is  of  special  interest  to  professional  men, 
as  lawyers  and  physicians,  it  is  valuable  to  all  who  are  interested  in 
the  phenomena  of  mind  and  the  problems  of  education. — Outlook. 

G.  P.  PUTNAM'S  SONS 
New  York  London 


f 


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